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The various primary vascular systems of shoots of Anagallis arvensis L. (Primulaceae) can be distinguished in relation to the number of leaves (two, three, or four) at each node. In this study, shoot segments (single internodes and the nodes above them) were examined. The arrangement of segments within shoots was also recorded. The vasculature forms a closed system with the number of sets of bundles usually equal to twice the number of leaves. Irregularities are found in the following features of the system: the number of bundles composing leaf half-traces; occurrence of anastomosing bundles; the number of internodes through which bundles extend; levels of leaf attachment to the stem at the node; and distribution of parenchyma within the vascular cylinder, which determines the number of bundles in sets and the number of bundle sets. The irregularities occur with different frequencies for segments exhibiting different phyllotactic patterns. Comparison of these frequencies leads to the following conclusions: anastomosing bundles occur only in decussate or trimerous shoot segments, whereas sets of bundles united within internodes and displaced leaves occur only in tetramerous or trimerous ones; decrease of the number of bundles per leaf and displacement of leaves at the nodal level are correlated; variation between segments exhibiting the same phyllotactic pattern is greatest for trimerous, less for tetramerous, and least for decussate segments; the vascular system of decussate shoot segments is more stable than that of the other systems; and trimerous segments seem to be intermediate between the other two segment types. The occurrence of different phyllotactic patterns during a plant's ontogeny is frequent in nature and well described

Crystals in 16 species of poisonous plants growing naturally in Saudi Arabia were studied with light microscopy. Three types of crystals were observed: druses, prismatics, and crystal sand. Raphides and styloids were not observed in any of the species studied. Druses occur more frequently in the leaf midrib and in the cortex and pith of the stem. In contrast, crystal sand and prismatic crystals are rare and occur in the leaf, intercostal lamina, and in the vascular tissues. The preliminary results show the absence of the three types of calcium oxalate crystals in the stem and leaf of seven species: Ammi majus L., Anagallis arvensis L., Calotropis procera Ait., Citrullus colocynthis (L.) Schard, Euphorbiapeplis L., Hyoscyamus muticus L., and Solanum nigrum L., and the presence of druses, prismatic crystals, and crystal sand either in the leaf and stem or in the leaves or stems of nine species: Anabasis articulata (Forssk.) Moq. in DC., Chenopodium album L., Convolvulus arvensis L., Datura stramonium L., Nerium oleander L., Ricinus communis L., Rumex nervosus Vahl., Pergularia tomentosa L., and Withania somnifera (L.) Dun. in DC. These observations indicate that there is no apparent relationship between the distribution of calcium oxalate crystals and the toxic organs of the plants, and supports the view that the presence of calcium oxalate crystals may not be related to plant toxicity.

Vegetative seedlings of the Ceres strain Brassica campestris L., a quantitative, long-day plant, were induced to flower by exposure to a 16-hr, long-day cycle. Cytohistological and cytohistochemical changes associated with inflorescence development were examined. Developing shoot apices were classified in vegetative, transitional, and reproductive stages. The vegetative apex possessed a biseriate tunica, central zone, peripheral zone and pith-rib meristem. The transitional stage at 48 hr was marked by an increase in size and by a stratification of the upper cell layers of the shoot apex with a concurrent decrease of apical cytohistochemical zonation. The reproductive stage was initiated at 58 hr by periclinal cell divisions in the 3rd and 4th cell layers of the flank region. Cytohistochemical zonation in the vegetative apical meristem was restored in the floral apex. An "intermediate developmental" phase was not observed between the vegetative and reproductive stage. FRIEND AND HELSON (1966) reported a quantitative, long-day Ceres strain of Brassica campestris L. that is highly sensitive to one photoinductive cycle four to five days after sowing. Anatomical descriptions of morphological changes associated with floral initiation in photoperiodic sensitive, long-day plants is limited to Lolium temulentum L. (Evans, 1958; Knox and Evans, 1966), Anagallis arvensis L. (Vaughan, 1955), and Sinapsis alba L. (Bernier, 1962). The morphological development of the inflorescence in B. campestris has not been studied except for the investigation by Chakravarti (1953) on the tunica-corpus organization in vegetative and reproductive shoot apices. Chakravarti did not in

We investigated the photoperiodic regulation of aging in Aiagcallis arvensis L. propagated by cuttings. Short-day (SD) conditions caused the persistence of juvenile forms and vegetative growth, as well as high rooting capacity and a high RNA content, through successive vegetative multiplications. SD + 1 long day (LD) every 15th day induced reproductive growth but allowed the persistence of a high rooting capacity and high RNA content through vegetative multiplications. LD conditions caused the persistence of the reproductive stage, the progressive loss of rooting capacity, and a decrease of RNA content. The longevity of the clones seems to be connected to the photoperiodic effects which induce indeterminate growth (SD) and/or determinate and reproductive growth. The loss of propagation capacity and the decrease of RNA content can be considered as indexes of aging not only in plants but also in