. L'anatomie développementale de l'Isoetes. L'Isoetes, la botanique. 28 L'anatomie développementale de l'IsoeteS. Fig. 10, 11, 12 et 13. Répartiteurs de plantes matures de 7. howellii comme vu dans des coupes longitudinales. Fig. 10 et 11. Répartiteurs montrant divisions périclines dans la couche superficielle de l'apex. X 400. Fig. 12 et 13. Répartiteurs de plantes plus grandes que celles de figues. 10 et 11, montrant une augmentation en nombre ou en largeur de cellule fichiers vers le sommet comme l'expression d'expansion latérale dans la région du sommet. X 350. Ces dérivés pourraient produire de nouvelles cellules à la fois verticalement et horizon- l'extrémité dans le tally

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. The developmental anatomy of Isoetes. Isoetes; Botany. 28 THE DEVELOPMENTAL ANATOMY OF IsoeteS. Figs. 10, 11, 12, and 13. Apexes of mature plants of 7. howellii as seen in longitudinal sections. Figs. 10 and 11. Apexes showing periclinal divisions in the superficial layer of the apex. X 400. Figs. 12 and 13. Apexes of larger plants than those of figs. 10 and 11, showing an increase in number or in width of cell files toward the summit as an expression of lateral expansion in the summit region. X 350. such derivatives might produce new cells both vertically and horizon- tally in the shoot tip. Mitoses and cell net patterns which indicate a contribution from the summit to the flanks of the apex have also been observed. Anticlinal divisions occur at the summit of the apex (pi. 6, B, at AS). The cell net pattern of an increasing number of files toward the summit in some apexes also leads one to believe that these apexes were growing in the summital region before the time of fixation (figs. 12, 13). The apexes of young plants consist of relatively few cells. The mitotic activity within the apexes of small plants cannot be accounted for by growth of the apex itself, because the size of the apex does not increase markedly in the first dozen plastochrons. The contribution from the apex to other regions of the shoot tip is more direct in small plants than in large ones. This contribution is indicated by the cell net pattern and by mitotic figures. The above analysis agrees in essentials with the accounts of Bruch- mann (1874) and Hegelmaier (1874), but in particulars supports Bruchmann's more restricted concept of a group of apical initials rather than Hegelmaier's concept of an apical cell surface. The group of apical initials present within the apex is distinguishable with certain staining. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not p

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