GNETALES 



399' 



thirty- two at the time of observation), the basal ones of which develop 

 numerous embryonal tubes that surround the lower part of the sus- 

 pensor, while the terminal ones (a plate of eight cells) develop the 

 embryo (fig. 454). The embryonal tubes are produced from the 

 same region that develops as a secondary suspensor in Ephedra, but 

 their function is not the 

 same. In germination 

 the young seedling of 

 Welwitschia (Bower 6, 7) 

 shows a well-developed 

 root, a very long hypo- 

 cotyl, and two small 

 cotyledons; and between 

 the root tip and the 

 hypocotyl there is de- 

 veloped a very conspicu- 

 ous footlike ("spade- 

 like," 28) process that 

 remains in the seed as a 

 haustorial organ. At a 

 later stage the cotyledons 

 become more conspicu- 

 ous, and the single pair 

 of persistent leaves ap- 

 pears associated with 

 them (fig. 455). 



The embryo-forma- 

 tion of Gnetum is a repeti- 

 tion of that of Welwit- 

 schia, at least in general outline. Lotsy's account (15) for Gnetum 

 Gnemon describes the extensive suspensor-like elongation of the ferti- 

 lized egg, the penetration of the endosperm in various directions, the 

 occasional branching of the tube, and the cutting-off of the embryo 

 cell, but does not follow the nuclear divisions. 



A recent investigation (25) of the same species has added some 

 interesting details. When the endosperm is fully developed, having 

 replaced the nucellus completely during the second season, its pe- 



FiG. 455. — Welwitschia mirabilis: a young 

 seedling, showing the cotyledons and the pair of 

 persistent leaves; the bilobed crown is evident just 

 above the insertion of the cotyledons; natural size. 

 — From photograph by H. Schenck. 



