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The rooting of cuttings from day-neutral tomato was not influenced by flower development, nor by SD or LD treatments of them or of the mother plants. In cuttings of the SD plant Perilla crispa flower initiation and development severely inhibited rooting. Leaves produced about 61 % of the roots, buds about 16 %, stems a small proportion. Together these organs were more effective than their summed separate effects. A supposed substance regulating adventitious root formation would need more than 2 days for transport from the leaves or buds. The physiological age of the cutting markedly affected rooting. The presence of buds during SD treatment may have changed auxin distribution, which became concentrated in the apical region and slightly promoted rooting there. Stems could induce flowering. Day length had no influence during rooting. Light on the base of the cutting inhibited root formation. In the LD plant red clover, flower initiation inhibited rooting of cuttings.In both SD and LD plants, auxin distribution during flower initiation and development must cause antagonism between adventitious root formation and flowering. This did not apply to day-neutral plants with a vegetative terminal bud, but perhaps to those with a terminal flower bud.

In mustard N deficiency accelerated flower initiation and particularly flower bud development. Excess N delayed flowering but increased number of flowers. Of other elements Ca influenced flowering most.Dill developed its flowers most rapidly with normal or high rates of N. N deficiency retarded flowering and decreased the number of inflorescenses.In spinach N rate only slightly influenced flowering. N deficiency retarded flower budding by a few days.Perilla crispa reacted most to N and P. Except where N was in excess (2N), the time required for appearance and development of flower buds was negatively correlated with the N concentration, while the number of flowers was positively correlated with it. P deficiency delayed flowering and decreased the number of flowers.With Kalanchoë blossfeldiana N increased the number of flowers and accelerated flowering.Mineral nutrition had only quantitative influences on the photoperiodic behaviour of the crops studied.It was concluded that the effect of minerals on the flowering process of LD (mustard, dill and spinach) and SD plants (Perilla and Kalanchoë) was indirect, through their effect on synthesis of material for flower bud formation, on auxin production and hence on growth.

Germination of pear pollen markedly improved when boric acid was added to the medium. The pollen was more sensitive to boron in water than in 10 % sugar solution. Supplying weak solutions of boron to pear branches before flowering resulted in a good germination of the pollen in sugar solution without boron. Spraying apple-trees and pear-trees with boron solutions had no significant effect on fruit set, despite the pollen sensitivity to boron in vitro.The amount of boric acid in the medium determined percentage germination (saturation curve) and length of pollen tubes. Boron was not required until the tubes protruded. Temperature and sugar concentration both showed optimum values for germination. The effect of boron on germination rate was positively correlated with temperature and negatively with sugar concentration. An increase of 10°C roughly doubled this influence on germination rate. Germination was positively correlated with pollen grain number per drop, whether or not boron was present. So the mutual stimulation of the pollen was more effective with boron or with pollen from rather boron-rich branches. Pollen extracts in 10 % sugar solution with or without boron stimulated germination (also of other species).Both apple and pear pollen (and those of many other species) remained viable longest at both low humidity and temperature. In deep-freeze longevity was more than 2 years at -180°. Viability remained unchanged. Longevity would probably have been indefinite.

A major problem in cauliflower is the occurence of buttoned plants in which vegetative growth was checked shortly after planting out. This results in too early formation of small curds of poor quality ('premature heading').It was found that this could be prevented by transplanting small plants. All factors favouring growth of the young plants in the seed-bed promoted buttoning.Spring crops should be sown late in the autumn and planted out early, whilst early quick-growing varieties should be sown later than late varieties. Plants should be kept cool and dry.Young plants for summer crops should be grown at rather high densities in the seed-bed. Through severe competition plants thus remained small and therefore less prone to buttoning after transplanting. Experiments on breeding showed that cauliflower could be inbred for several generations without any deleterious effect. Seed-setting after selfing was normal and the crop therefore should be considered as self-fertilizing. This was confirmed by field experiments.For selection after July plants must be propagated vegetatively. A method of obtaining cuttings from shoots developing on the stem base and roots was described.Male-sterile plants were found at a rate of 0.05 %. It was determined by a single recessive factor.Earliness was positively correlated with leaf number (r 0.9017).Firmness of the curd was related to its structure and was determined by recessive genes. Plants with poor curds yielded more seed than plants with firm curds.

The initiation of new flower buds in Pelargonium zonale Ait. was strongly inhibited by GA 3 . The duration of development of the initiated umbel was diminished and the stalk of the umbel elongated. The winter dormancy of the flower buds of Convallaria majalis started earlier with a dry or warm cultivation and by GA 3 during the growth or during storage. GA 3 was not able to break winter dormancy of the buds without previous cold treatment.After castration and GA 3 treatment of some varieties of pears many treated flowers set fruit parthenocarpically. After night frosts in 1960 and 1962 a considerable fruit set was obtained from severely frosted flowers after GA 3 treatment of pears. Thus night frost damage to pears could be controlled with GA 3 .The induction of parthenocarpy in apples with GA 3 did not succeed, neither after castration or after night frost. A possible improvement is the use of other gibberellins, especially GA 4 . The presence of seeds in the fruit proved necessary until the June drop. Undesired effects of GA 3 may be a decrease in the number of flower buds or abnormal fruit shape.The growth of the heads of unchilled roots of Belgian chicory was strongly stimulated by GA 3 . GA 3 treatment increased the number of male flowers in cucumber, favoured the bolting of spinach, hastened the ripening of tomato fruits, but did not favour the growth of the fruits of Solanum melongena and Capsicum annuum.

Cytological studies and crossing experiments were carried out in both cultivars and species of Cyclamen in connection with breeding. Within 278 groups of Cyclamen cvs. grown at different nurseries in Western Europe, there were 48 diploids with 2n = 48, 168 tetraploids with 2n = 96, 58 and 4 aneuploids with 2n = 92 and 94, 95, respectively. It was known that the first tetraploid and aneuploid originated in 1863 and 1898, respectively.The results of reciprocal crosses between diploids and tetraploids were studied. On genetic evidence the origin of the unexpectedly high number of tetraploid descendants was explained by dispermy (fertilization of the female gamete by two male gametes) in the cross 4n x 2n and analogously by endogamy (fusion of 2 haploid embryo sac nuclei) in the 2n x 4n cross.The chromosome range of 14 Cyclamen spp. was determined as 20, 22, 30, 34, 48, 84-86, 96 and 136, to be grouped into 3 polyploid series with the basic numbers n = 10, 17 and 24. Attempts to produce interspecific hybrids failed, except once. Reconstruction of some numbers and creation of missing links by crossing the present-day species was therefore impossible.

Graft combinations were made between flowering (donor) and non-flowering (receptor) plants, and grown in a photoperiod unfavourable for flowering of the receptor.Donor leaves of the short-day (SD) plant Perilla crispa caused a maximum flowering response after exposure to 30 SD. By the use of radioactive sucrose it was shown that a functional phloem connection between donor and receptor was necessary for transmission of the floral stimulus. Induced Perilla leaves transferred to LD had not lost their capacity to induce flower formation after 3 months. But leaves taken from flowering receptor branches did not function as donors. Thus, photoperiodic induction of Perilla was permanently conserved in the SD-treated leaves. This was in contrast to Xanthium (SD plant) in which indirectly induced shoots could themselves transfer the floral stimulus to receptors.Transmission of the floral stimulus was also demonstrated between: Kalanchoë (SD plant) and Sedum (LD plant), and between Maryland Mammoth tobacco (SD plant) and Nicotiana sylvestris (LD plant). In either case, the LD plant as well as the SD plant could function as donor for the other partner. A day-neutral tobacco variety did not cause flower formation in Maryland Mammoth tobacco, but when grafted as interstock between N. sylvestris and Maryland Mammoth tobacco it permitted transfer of the flowering stimulus. It was concluded that in graft-compatible species the floral stimuli of SD and LD plants seemed to be identical.

Directives were drafted for different aspects of wind protection and shelterbelts. An analysis was made of the effects of wind and protection on crop yields, and the establishment of shelterbelts was discussed. The respective increases in yield of bean and maize crops, in the protected zone of the windbreak in the experimental field, were only 12 and 17 % in 1960 by accumulation of moisture behind the windbreak, through excessive rainfall and partial rotting of the bean plants. For maize a height and width of windbreak of 2 m and 6 m, respectively, was too small.In a wind tunnel in a greenhouse the yield of bean seed was 67 % higher in the protected zone. In pot experiments the respective yields of bean seed and dry weight of maize plants increased by 28 % and 11 %.The optimum shelterbelt design was estimated by models in a wind tunnel. Shelterbelts mainly improve temperature, transpiration rate and soil moisture conservation, and also prevent mechanical injury of plants. This results in an increased photosynthetic surface and a better relation shoot/root. The Shamin shelterbelt model proved best for large areas, the Ali and Usman models for smaller ones. The planning, administration and management of shelterbelts were discussed.

Premature formation of tubers ('submarines') is a disturbance in the normal growth of a planted seed potato, resulting in the formation of some small daughter tubers without any aerial growth. In certain years losses may be heavy. The main cause is the formation of sprouts during storage which have to be removed. All factors preventing or reducing such sprout formation favour normal development: especially low temperature (above freezing-point) and light during storage, also late lifting of the seed tubers, large tubers, planting at higher temperature and in moist soil.The underlying process of premature tuber formation was assumed to be loss of water by removal of sprouts during storage, resulting in an increase in the concentration of solutes. Essentially the same occurs with normal tuber formation but there by an increase in assimilates. This concept was supported by plasmolysis studies in the hairs of the sprouts.

The two main factors for bolting and flowering of endive were temperature and light; their influence on both growth and development was investigated.From experiments with successive dates of sowing, different raising temperatures and different growing conditions the following facts emerged: with increasing raising temperature, crop weight increased by delayed bolting; extra light during the seedling stage, or short day during the seedling stage, delayed bolting, but did not always increase crop weight; after the raising period, high temperature stimulated bolting and increased crop weight.Low temperature (5°C) during germination or in the seedling stage promoted bolting and flowering; in short days, vernalization accelerated bolting considerably; in long days, it depended on the age of the plant at the time of vernalization. Interruption of seed vernalization by normal temperature delayed bolting. The effect of seed vernalization, if applied for a limited period, could be nullified by high temperature (35°C) immediately after vernalization.In unvernalized plants grown at 35°C bolting was accelerated. Increasing day length promoted early bolting. The only flower-promoting action of short days had been observed when short days preceded vernalization.Low light intensity promoted or inhibited bolting, according to other factors.

Investigations on the flower induction were carried out with Silene armeria L., a plant species flowering under all conditions after a treatment at LD, 5° C or 32° C. Two strains E 1 and L 1 differing in their photoperiodic and temperature requirements, were used in the present research, which completes former investigations (VAN DE VOOREN 1969a, b, 197 1 a, b).High temperaturePlants under short day conditions at 32° C are induced to flower bud formation. A quantitative juvenility for 32° SI), interaction between 32° SD and L 20° , partial induction by 32° SD and desinduction of this partial induction in SD 20° exist in both strains, but E 1 is more sensitive than L 1 .High temperature action on flower induction is maximal during the middle of a 16 h dark period for both E 1 and L 1 . Maximal action in E 1 is more precisely 7 h after the onset of darkness, independent on the length of the dark period for 8-16 h photoperiods. There is no action for 20 and 24 h photoperiod.No influence of temperatures on flower induction during SD is apparent in the range 10°-30°C and an increasing response in the range 35°-50° C.LightLight intensity is an important factor in flower induction. Increasing light intensities during SD or CL increase the flowering response. The optimal light intensity during CL is rather low in E 1 and has not been reached in L 1 in our experiments.Photoperiodic response curves at 20° and 32° C for E 1and L 1For photoperiods from 8 to 18 h more numbers of cycles necessary for 50% flowering are needed for 20° C than for 32° C. The curves run parallel for both E, and L, at photoperiods from 18 to 24 h. In this range E 1 needs an equal number and L 1 decreasing numbers of cycles.HypothesisThe mechanism of flower induction is a balance between two processes:1. A deblocking process in high intensity light, increasing light intensities accelerating it with an optimum, temperature insensitive.2. A reblocking process in darkness, starting about 4 h after the onse

Influences of genotype (cultivar), temperature, light intensity, gibberellic acid (GA 3 ) and daylength on stem elongation and flowering of spinach were investigated. Most cultivars reacted quantitatively to long days (LD) both for stem and flower formation. Daylength requirements varied from almost dayneutral to LD.Cold, 2-8°C, decreased daylength requirement; 9-12° only accelerated stem growth. All cvs reacted similarly to temperature. Dimmer light decreased daylength requirement, especially in later cvs. GA 3 accelerated stem growth strongly, flower- formation only slightly.There was no juvenile stage for temperature or daylength response. Regression of flower formation may occur in a qualitatively LD cv after transfer to SD. Flower formation was most inhibited with photoperiods of 6-10 h; it increased with shorter or longer photoperiods. A qualitative LD cv as 'Nobel' remained vegetative only in SD, if stem growth was inhibited. In SD differentiation in axillary primordia and the consequent formation of flower clusters occurred much slower than in LD and stopped early unless caulescent tissue grew at low temperatures, dim light or GA 3 in accordance with the hypothesis of Chailakhyan that both gibberellins and floral stimulus were needed for stem growth and flower differentiation, respectively, of LD rosette plants. Formation of both hormones would depend on daylength.Cvs were earlier where they required shorter daylength and where they grew faster. By studying the influences of temperature, vernalisation, light intensity and GA 3 on yields, through their influence on developmental rate and growth rate, several practical conclusions could be drawn about optimum sowing date.

With an annual production of about 250 000 to 300 000 tons, onion (Allium cepa L.) is the most important outdoor vegetable crop in the Netherlands. The greater part, namely 70 to 80 %, has to be exported, and is meeting increasing competition. For this reason and in connection with changed growing and handling methods, including mechanization, there is a need to breed improved varieties.Breeding-work with the biennial onion, however, takes much time and shortening of the breeding cycle would be very profitable. This has been the purpose of the present research. By means of literature data, all phases of growth and development .have been investigated. Flower induction and initiation appeared to be dependent on temperature, but not on day length.At first we tried to promote rapid flowering of the bulbs by means of temperature treatments (chapter 3.1). This did not give satisfactory results. Development was very irregular and slow and only exceptionnally all the plants became generative (table 3). Nevertheless, we obtained more information about the factors required for development. We showed that the optimum temperature for flower induction for the cultivar "Rijnsburger" is 9° C rather than 13° C (graph 4). Moreover, short heat treatments before and after the storage period stimulate the regrowth (graph 2), but counteract the floral development (antivernalisation and devernalisation). This explains why the yield of seeds after storage of the mother bulbs under supra-optimal temperatures is lower than after storage under sub-optimal temperatures.Abortion of the young scapes (flower stalks) occurs exclusively under long days and to a greater extent at high temperatures (table 6). Our observations indicate that abortion is dependent on the distribution of assimilates between the scape and an axillary bud (photo 3). A "bulb/flower competition hypothesis" was formulated in the sense that, just as with onions grown for bulb production, in long days and at higher temperature

1. The problem. In propagation for summer planting the plant material generally will not be available in time to the growers. As the cause was not known, the question arose whether the reproducibility of the varieties was sufficient.2. Experimental procedure. The factors for reproducibility were ascertained. To this end an analysis was made of the factors determining the number of salable plants. This investigation consisted of three parts, which can be summarized as follows.3. Number of salable plants per mother plant. As the number of rooted runners increases, more runner plants per mother plant are formed (Tables I, p. 14, and 3, p. 16).The optimum temperature for the growth of the sprout of a runner plant is higher than the temperature at which the propagation is done in the Netherlands (Fig. 3, p. 21, and 4, p. 22). The optimum temperature for the development of the root initials falls within this range (Table 5, p. 25). As for the establishment of strawberry plantations preference is given to plants with a not too heavy sprout, the temperature in the Netherlands is generally favourable for a rapid production of salable plants. Under good cultural conditions more salable plants are formed as the total number of runner plants formed becomes larger (Fig. 6, p. 26)The number of rooted runners increases as the total number of runners formed is increased (Fig. 7, p. 28).Therefore the number of salable plants formed by a mother plant is determined by the total number of runners formed, on the basis of the following considerations:1) number of runners ->number of rooted runners2) number of rooted runners ->number of runner plants3) number of runner plants ->number of salable plants.An exception is the variety Senga Sengana. It forms many runners, but the number of salable plants per mother plant is comparatively low, because only few plants per runner are formed (Table 3, p. 16). This is caused by:a. The phenomenon that in many runners at the base of the second or thi

The factors, influencing the synthesis and action of floral hormones, and possible differences between floral hormones in different plants were studied. The experimental results are summarized in the conclusions 1-20, on pages 35-36 (Crassulaceae'); 21-39 on pages 58-59 ('Xanthium strumarium') and 40-50 on pages 74-75 ('Caryophyllaceae').General conclusions are as follows:1. The processes leading to flower formation of plants with a floral hormone can be roughly divided in induction and realization, the latter subdivided in synthesis, transport and action of floral hormone as initiation of flower buds in the receptive meristems. These processes are called the 'floral chain'.2. In the long-short-day plant Bryophyllum daigremontianum neither the LD, nor the SD induction were influenced qualitatively by temperature, but the resulting inductive state and the already synthesized floral hormone were destructed by too high a temperature.3. In the short-day plant Kalanchoë blossfeldiana the induction was influenced by temperature, so that in individual species different processes of the floral chain may be influenced.4. In the LSDP B. daigremontianum no 2 separate components of the floral hormone are formed.5. The transmission of floral hormone by grafting is influenced by the direction of movement of the hormone in B. daigremontianum and by the age of the receptor in the SDP Xanthium strumarium. Presence of the leaves in X. strumarium strongly stimulates the growth of the axillary shoots and reduces the flowering-reaction, while defoliation of receptors promotes the transmission of flowering.6. In K. blossfeldiana and X.strumarium early lines need less floral hormone for a flowering-reaction than late ones. The former have a lower threshold value of the hormone.7. The good donor capacity of B. daigremontianum towards K. blossfeldiana in contrast to the reverse combination suggests a lower level of floral hormone in K. blossfeldiana than in B. daigremontianum.8. Also in X.

An analytical study of the cyclic stomatal behaviour in leaves of bean, Phaseolus vulgaris L. 'Vroege Wagenaar', was made in order to explore the cycling, to study different aspects of plant water relations and of the action mechanism of the stomata. A general method of investigation was recording of the difference of temperature of leaf and air with thermocouples in a constant environment.Introductory observationsPlants grown at low light intensity showed a higher tendency to sustained cycling (higher instability of the stomatal apparatus) than those grown at higher light intensity. At the higher light intensity non-aeration of the nutrient solution increased the tendency to cycling with a more than additive effect. It is suggested that the lower capacity to take up water of non-aerated roots was involved in the higher tendency to cycling. Cycling over the whole plant was frequently disturbed by bringing cycling of a part of the active stomata out of phase. Cycling was induced by changing abruptly any factor that affected stomatal opening, by entrainment with cycling air vapour pressure, by entrainment with cycling plant water potential, and apparently spontaneously.Younger leaves showed shorter free-running periods than older ones. When both were attached on the same plant, cycling in the younger leaves entrained cycling in the older ones.Water relations of cyclingAmplitudes of cycling increased by decreasing air humidity and by increasing the water potential in the root medium. A time delay in the adjustment of the turgor of the guard cells to the plant water potential is assigned to be the cause of overshooting of the active stomatal movement and as to be the factor amplifying both passive opening and closing movement. Cycling only occurred when an important resistance to water uptake was present in the transpiration stream. In intact plants this resistance was located in the roots. The water potential cycled in the whole plant down to this resistance, synchroni

To study possibilities for increases of yield of the apple cultivar Cox's Orange Pippin, relevant information was gathered about fruit set and fruit drop, in particular about June drop. The information concerned pollination intensity, amount of fruit set, seed content of the fruit, number of leaves per spur, and the influence of the bourse shoots. Several growth regulators were tested to see whether these can reduce June drop.The main conclusions drawn from the results of these observations are given in Section 3.1.3. (p. 18). The growth regulators examined were NAA, NAAm, GA 3 , GA 4+7 , BA and ABA. The experimental results are given in Section 3.2.3 (p. 40). The most interesting finding in the latter part of this work was the promising ability of GA 4+7 to reduce June drop.The factors underlying fruit set, fruit drop, and fruit growth and the possible role of the applied regulators under study are discussed, whereby fruit drop was related with leaf abscission.

In the spring of 1965 a trial was planted with Golden Delicious IX and James Grieve 'aimed' VII, in which tree spacing, deblossoming, Alar sprays and pruning were variable factors, Results are presented over the period 1966-1969.At the end of 1969, the 5th year from planting, 400 Delicious trees and 160 'aimed' trees were grubbed to measure tree weight and foliation. Tree weight was closely correlated to trunk diameter; for a given diameter pruned trees weighed slightly less than unpruned trees. The relations of leaf weight and leaf area per tree with trunk diameter were less well defined and varied more for different treatment combinations; the same applied to the relations of shoot number and total shoot length over 1966-1969 with trunk diameter at the end of 1969.The grubbed trees were also used to collect data on dry matter yield for Delicious IX. Estimated dry matter yield per unit area in 1969 still increased with density, largely as a result of increasing 'leaf area indices'. Fruiting greatly enhanced dry matter yield per unit foliage and more than 50% of dry matter yield was recovered in the fruit. Pruning also tended to stimulate dry matter yield per unit leaf area; it raised the share of dry matter accumulated in the tree frame, at the expense of the share for leaves and fruit. A large proportion of dry matter increment in the tree frame was removed by pruning.Inter-tree competition at close spacing manifested itself in reduced growth and yield per tree, in lower yields per unit growth, in a reduction of mean weight per fruit and in the tendency of the trees to become top-heavy as a result of accelerated height growth and suppressed growth in the basal portion of the trees. These effects became more prominent with increasing age, suggesting that at the closest spacings it will be difficult to control growth and to prevent yield depressions as the trees get older. This leaves the superiority of yield during the early years of orchard life as the main advant

A study was made of changes in fast neutron effectiveness during the hydration and germination of tomato seeds. The main findings and conclusions are the following,Section 3.6Samples of unirradiated seeds and their constituent parts (seedcoat+endosperm and embryo) were taken at short intervals up to 72 hours after sowing, and samples of roots, hypocotyledons and cotyledons from 72 to 144 hours after sowing. Their water content, dry weight and elementary composition (C, H, N, O and Ash) were determined.At 27°C, the water content reaches a 'plateau' after ca 20 hours. Further uptake depends upon the rupture of the seedcoat as a result of internal forces developed by metabolic processes. This post-germination water uptake is exponential until the 'saturation' phase, but it commences much earlier in the root than in the hypocotyledon and only much later in the cotyledons. This sequence corresponds with the time of liberation from the seedcoat.Appreciable changes in the dry weight of the embryo and the endosperm commence ca 8 hours after 50% germination. These comprise the resorption by the embryo of 75% of the dry matter of the endosperm (completed ca 60 hours after 50% germination) and de novo synthesis. At 104 hours after 50% germination, the former process has contributed 2/3 and the latter 1/3 to the total dry weight increase of the seedling. The increase in dry matter occurs first in the cotyledons (resorption of endosperm) and commences only ca 24 hours later in the other parts of the embryo. Approximately 56 hours after 50% germination, the dry weight of the cotyledons reaches a maximum after which it decreases; at this time the dry weight of the other organs increases rapidly.The elementary composition of the dry matter is static until germination (apart from an early increase in N, by KNO 3 uptake from the medium). Subsequently, the C and H contents decrease markedly in all parts of the young seedling, while the N, O and Ash contents increase. These changes com

Rede. Wageningen, 9 maart 1959

Having established that cut flowers last longer by adding such solutions as sugars, bactericides or acids to the vase water, their mechanism of action was investigated.Bacteria and fungi had a direct plugging effect, but also acted indirectly on the water conduction of the flower stalk by secreting toxins. A third kind of plugging occurred independent of micro-organisms as a reaction to wounding and intrusion of air. This plugging could be limited by reducing 02 concentration, lowering the pH and by adding Ca(N0 3 ) 2 .The addition of sugar prevented disintegration of cells through lack of respiratory substrate. In times of higher respiratory activity of the flower parts, the optimum sugar concentration needed in the water increased.Attempts to decrease respiratory activity of the flower by adding respiratory inhibitors failed. Only in Matthiola could the respiratory activity be decreased by gibberellic acid; at the same time the flowers lasted longer.Boron had a favourable effect in Convallaria, Dianthus, Lathyrus and Syringa. Its addition decreased the optimum sugar concentration. In Dianthus it acted on the distribution of dry matter within the flower during development.The possibilities were discussed of practical application of chemicals to make cut flowers last longer.

Tulips did not require a specific soil, if pH was not below 6.5 and water supply was sufficient. Influence of weather conditions was studied by comparing bulb production in different years and areas. Low temperatures after planting and during winter, a gradual increase in spring, sunshine in April and early May, were most favourable. Cold during May and June caused some extension of growth and increased bulb productions.Records of daily weather conditions and growth yielded no correlation with radiation and temperature and with precipitation, except after drought. Increase in circumference was positively correlated with the length of period with a limited evaporation and transpiration. Growth therefore took place during the night while dry and hot days decreased bulb size.In conclusion the most favourable conditions for bulb production were an early winter and a long cool spring, and circumstances limiting transpiration of the crop. Of these environmental conditions only evaporation could be influenced and for this purpose shelter belts of conifers were recommended.