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The evolutionary significance of a mixed mating system is currently under debate. Calluna vulgaris (L). Hull, a widespread European shrub, is likely to undergo mixed mating because of geitonogamy. Mating system was investigated in three populations of C. vulgaris by means of greenhouse controlled crosses, pollen tube observations, and outcrossing rate estimations from allozyme markers. The species is highly self-sterile, most probably as a result of early inbreeding depression. Mean fruit set and mean seed number per fruit following hand self-pollination were 48 and 13%, respectively, of those following cross-pollination. Pollen tubes produced by self pollen penetrated the ovary with the same success as those from cross-pollination. Multilocus estimates of the outcrossing rates ranged from 0.71 to 0.90, and two estimates were significantly different from 1.00. Calluna vulgaris could thus be classified as being mixed mating with predominant allogamy. Single-locus estimates did not differ significantly from multilocus estimates suggesting that biparental inbreeding did not contribute to the apparent selfing rate. The maintenance of high early inbreeding depression despite an intermediate level of selfing is discussed with respect to recent theories on mating system evolution. Key words: Calluna vulgaris, mating system, self-sterility, pollen tubes, outcrossing rate, inbreeding depression.

Stigma and style morphohistological features of the six Romulea species (Iridaceae) living in France and their various pollination modes, described for the first time in this study, were considered with regard to nectar floral apparatus features, also described for the first time here. This apparatus was also variable among taxa. The results confirmed the self-compatibility of all species as well as the almost obligate autogamy among the small-flower species, and the allogamy among the gynodioic large-flower species. This study represents a new and necessary step in the reconstitution of the speciation and genus evolution. Keywords: Romulea, reproductive systems, autogamy, allogamy, evolution, speciation. [Journal translation]

Male fertility variation in an open-pollinated plantation of Norway spruce (Piceaabies (L.) Karst.) was studied using six polymorphic isozyme marker loci. Significant variation in male fertilities was detected in the seed crops from 81% of the female parents. The ranking of relative contribution of male parents to the offspring varied considerably among seed crops. Pronounced heterogeneity among the fertility estimates of a male parent derived from different seed crops was also observed. The overall male fertility estimates were highly skewed, with less than 23% of trees contributing more than 50% of the male gametes to the seed sample. In addition to postpollination mechanisms, factors associated with pollination such as variation in pollen production and floral phenology among trees likely have contributed to the observed male fertility variation. These results have significant implications in forest tree improvement programs.

Arrays of open-pollinated seeds were assayed for allozyme polymorphisms at four loci (Mdh-1, Me, 6Pg-2, and Pgm) to obtain estimates of outcrossing rates for three eastern white cedar populations in northwestern Ontario, Canada. Multilocus population outcrossing rate estimates were low, ranging from 0.507 to 0.745, with significant heterogeneity among populations. Low stand densities and relatively high selfed embryo survival may have contributed to the low effective outcrossing rates observed. Single-tree multilocus outcrossing rate estimates were obtained for nine trees from one population. When estimated jointly with outcross pollen pool allele frequencies, these outcrossing rate estimates ranged from 0.253 to 1.023 with significant heterogeneity among trees. Key words: mating system, outcrossing rate, Thuja occidentalis L.

The effects of self-, cross-, and no pollination on cone size, filled seed, pollination efficiency, ovule development, and seed efficiency were tested on rooted ramets of six western red cedar (Thujaplicata Donn) clones. To fully develop, ovules must be pollinated with viable pollen and cones must have a minimum of one developing seed. The seed potential was constant among clones and not affected by pollination. The greatest loss of potential seed resulted from a failure of ovules to be pollinated, followed closely by the low percent viability of pollen. Unpollinated ovules aborted at the megaspore or free-nuclear stages. Pollinated ovules may abort at any stage of development, but it was most common during the long free nuclear stage. Selfing had a limited effect on postzygotic loss owing to embryo abortion or on seed set. Western red cedar is well adapted for a high degree of selfing. Clonal differences occurred in seed efficiency and stages at wich seed losses were most commun. Seed set in western red cedar may be increased if cones on female parents having a history of high seed efficiency are pollinated several times within a 1 week peak pollination period with abundant pollen of known high percent viability. Potential seed losses are discussed with reference to pollination and ovule development.

The breeding system and determinants of fruit and seed production in a population of 114 patches of Mayapple (Podophyllum peltatum L.) were examined. Experimental crosses indicated that Mayapple patches are self-incompatible (clones) and that fruit and seed set were pollinator limited. Mayapple flowers are nectarless yet depend primarily on infrequent visits by nectar-searching bumblebees for pollination. The proportion of flowers setting fruit and ovules setting seed in Mayapple clones was inversely associated with the distance to neighboring clones and the distance to Pedicularis canadensis L. plants. Clones within 45 m of P. canadensis plants (which are heavily visited by bumblebees) showed significant increases in fruit and seed production compared with a similar group of more distant clones. This effect is interpreted as evidence for a facilitative interaction between Mayapple and P. canadensis.

Factors affecting reproductive strategies of pearl millet, which is currently classified as a predominantly allogamous species, were investigated. Gametophytic competition as well as the effect of growth temperature on this phenomenon were studied by means of the pollen mixture technique. The relative competitive ability of pollen from five different genetic stocks (Ligui, Massue, "Chinese," Thiotandé, 23d2B) was assessed by isozyme electrophoresis (esterase, alcohol dehydrogenase) of progeny plants. Gametophytic competition with a polygenic inheritance trend for pollen competitive ability is reported. A better competitive ability of autopollen on various types of allopollen was systematically found for the Ligui genotype. Temperature stress enhanced this trend. Hypotheses on the role of gametophytic competition in the evolution of the primary genetic pool of P. typhoides are discussed.Key words: pearl millet, pollen, competitive ability, segregation distortions.

This paper is concerned with insect visitors to some Canadian weeds. It shows that both self-pollinating (autogamous) and cross-pollinating (allogamous) weeds are visited during the flowering period. It was found that self-incompatible species were visited by insects frequently, whereas self-compatible weeds were not visited or were rarely visited. The self-compatible group showed some difference, in that autogamous annual and winter annual weeds were visited less than were autogamous biennial and short-lived perennial weeds. Most of the insect visitors, to both the autogamous and allogamous species of weeds, were native species, whereas the weeds themselves were mostly introduced species. The insects, also, evidently visited more than a single species of plant over a short period of time. The implications of the insect visits to the genetic structure of the plants and their colonizing abilities are then briefly discussed.