Image d'archive à partir de la page 80 de l'anatomie développementale de l'Isoetes. L'anatomie développementale de l'Isoetes . developmentalana31paol Année : 1963 Racine Racine Primaire Primaire Fig. 24 et 25. Représentations schématiques de la position relative des six premières racines de les sporophytes de Isoefes. Les emplacements sont provisoirement placées en série et en orthostichies. Fig. 24. L'emplacement des premières six racines de I. laciisfris selon Hofmeister (1862). Les sites d'initiation des racines de deux orthos- tichies peut être en phase dans la production de primordia sur alteiTiate côtés du méristème basal. Fig. 25.

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Archive image from page 80 of The developmental anatomy of Isoetes. The developmental anatomy of Isoetes . developmentalana31paol Year: 1963 Primary Root Primary Root Figs. 24 and 25. Schematic representations of the relative positions of the first six roots of sporophytes of Isoefes. The locations are tentatively placed in series and in orthostichies. Fig. 24. Location of the first six roots of I. laciisfris according to Hofmeister (1862). The sites of root initiation of two orthos- tichies may be in phase in the production of primordia on alteiTiate sides of the basal meristem. Fig. 25. Location of the first six roots of /. engelmanni according to Baldwin (1933). The sites of root initiation for all three orthos- tichies may be in phase in the production of root primordia on alternate sides of the basal meristem. of the furrow as the first root (fig. 25). The variability of the patterns of initiation in young plants has not been assayed and the exact relation- ship of the pattern of initiation in young plants to the pattern in mature plants is not known. Attention may now be given to the curvature seen in series and orthos- tichies in cross-sections taken at various levels of the plant (figs. 15-18). One might expect that the lines connecting the series would converge toward the x-axis in transverse sections, because of the bidirectional and acropetal sequence of root initiation. The primordia are displaced from the basal meristem after they are formed, and the oldest member of a series should be displaced the farthest from the median plane. The ex- pected spatial arrangement is found at low levels in the plant, but not at high levels. To explain this variation, one needs to acknowledge that the basal meristem lies in a plane that is convex when viewed from below. The attachments of roots in the 0-orthostichy are encountered first in serial transverse sections taken in an upward sequence in a plant,

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