140 



EMBRYOGENESIS IN PLANTS 



After the octant phase, the initially squat embryo becomes globular 

 and then elongated vertically and its bipolar character becomes 

 apparent. The first root is formed endogenously near the centre of the 

 embryo when the latter has attained to some considerable size, a group 



Fig. 32. Embryogeny in Marattiaceae 



A, B, Aiigiopteiis evecta. A, Endoscopic embryo, with elongated suspensor {sii), 

 and small embryonic cell as seen in a transverse section of the prothallus; the 

 archegonium (a) is seen in l.s. B, A later stage, showing the embryo, with suspensor 

 («/), pushing inwards to emerge on the upper side of the prothallus (after Land). 

 C, D, Marattia dotiglasii. C, Young embryo; no suspensor is present, but the 

 embryo is endoscopic; I-L first partition wall; s, shoot; /, foot. D, An older 

 embryo; i, shoot apex; /, leaf; /), prothallus; o, archegonium neck ( x 100). E, 

 Augiopteris evecta. No suspensor is present. ¥, Daiiaea jamaicensis. A small sus- 

 pensor {sii) is present; I-L first wall of embryo; s, shoot apex; /, foot (C-F, after 

 Campbell). (A, x 200; B, x 100; C, x 225; D, x 72.) 



of cells dividing actively and becoming so organised as to constitute a 

 root apex, with a single apical cell of variable form. As this root 

 enlarges it penetrates downwards through the foot which becomes more 

 or less obliterated, and through the lower side of the prothallus into 

 the soil. This root development is more or less in organic continuity 

 with the first leaf. 



The second leaf is formed on approximately the opposite side of 



