. Texte-livre de botanique, morphologiques et physiologiques. La botanique. 42<5 des cryptogames. que ce dernier reste pendant un certain temps enfermé dans une protubérance issu de la surface, jusqu'à la première feuille et les briser. La première traite de la division de l'oospore sont, comme Hofmeister a montré dans le cas de la jetée est aquilina et Aspidium filix-mas, pas tout à fait semblables dans différentes fougères1. Il est certain, cependant, que la première division-mur (appelé le mur de base) de l'oospore est transversal à l'axe longitudinal du prothalle, et enclin à montrer comme il l'oblique ;

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. Text-book of botany, morphological and physiological. Botany. 42<5 VASCULAR CRYPTOGAMS. that this latter remains for some time enclosed in a protuberance springing from the under surface, until the first leaf and root break through. The first processes of division of the oospore are, as Hofmeister has shown in the case of Pier is aquilina and Aspidium Filix-mas, not entirely alike in different Ferns1. It is certain, how- ever, that the first division-wall (called the basal wall) of the oospore is transverse to the longitudinal axis of the prothallium, and inclined to it obliquely; as shown in Fig. 295, E, its inclination is the same as that of the neck of the archegonium. It is also certain that each of the two daughter-cells is' at once divided again by a wall in the plane of the prothallium (called the iransverse wall), so that the embryo now consists of four cells placed as quadrants of a sphere, and these are further divided by a wall parallel to the long axis of the prothallium (called the median wall). In Fig. 296 these first transverse divisions are indicated by thicker lines, the embryo being seen in longitudinal section. The explanation of the figure points out the interpretation which Hofmeister gives to the first four cells of Pteris aquilina, which the reader may compare with the corresponding development of Salvinia and Marsilia; but it must not be forgotten that the embryo of the Fern lies, so to speak, on its back. Although it is impossible in this place to go into a more. FIG. 296.—Vertical longitudinal section of the embryo of Pteris aquilina (after Hofmeister, Entwickelung und Bau der Vegetationsorgane der Fame, p. 607); the thicker lines are sections of the first two division-walls by which the embryo is divided into four cells (the continuous thick line represents the basal wall). The lower anterior cell forms the leaf b from the upper anterior is derived the stem st; from the lower posterior cell is produced the root, sw being its apical

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• bookcentury1800
• bookdecade1880
• booksubjectbotany
• bookyear1882