GNETALBS 



131 



verse division and other longitudinal divisions follow, until a 

 pyramidal mass of cells is organized at the end of the suspensor. 

 From the basal cells of this mass the embryonal tubes develop 

 (Fig. 92). No details of the organization of the various growing 

 points are given, but the completed embryo consists of a well- 

 developed root and a long hypocotyl, between 

 which there is organized a very conspicuous 

 footlike process, that remains in the seed dur- 

 ing its germination. Two cotyledons are de- 

 veloped, as in all Gnetales. 



Gnetum. — According to Lotsy,^^ the free 

 oospores develop long tubes, which advance 

 toward the mass of antipodal endosperm and 

 penetrate into it deeply, sometimes branch- 

 ing. During this advance the nucleus keeps 

 in the tip of the tube (Fig. 91, K). There is 

 every reason to suppose that this is a repeti- 

 tion of the behavior noted in Tumboa. It 

 is after this penetration of the antipodal re- 

 gion that the endosperm renews its growth 

 and finally encroaches upon the whole nucel- 

 lus. It is in this condition, with the tubular 

 oospore, containing the nucleus in its tip, im- 

 bedded in the antipodal endosperm, that the 

 seed drops. Lotsy reports that occasionally 

 the tubes are not directed toward the antip- 

 odal region, but may pass out of the micro- 

 pylar chamber into the nucellus, or may grow 

 directly away from the antipodal region. In 

 either of these cases there is no further de- 

 velopment. 



The further development of the embryo 

 of Gnetum Gnemon has been studied by 

 Bower.^ At the tip of the oosporic tube an embryonal cell is 

 cut off. This cell divides longitudinally and transversely, until 

 a small group is organized (Fig. 93, A), the basal cells of 

 which give rise to embryonal tubes, just as in Tumboa. The 

 mature embryo also resembles that of Tumboa in its two coty- 

 ledons, and prominent hypocotyl and root between which a con- 

 spicuous foot is developed (Fig. 93, B). 



Fig. 92. — Tumboa : a. 

 young embryo con- 

 sisting of a pyram- 

 idal group of cells, 

 the basal ones giv- 

 ing rise to embry- 

 onal tubes. — After. 

 Stbasbukgee. 



