82 ip o s t e I 5 i a 



cause which has led to embryonal propa- 

 gation (polyembryony) in many species. 

 The embryos of Gnetum, Welwit- 

 schia and probably of Ginkgo and the 

 Cycads produce true cotyledons which 

 remain in the seed during germina- 

 tion. While the embryos of Gnetum 

 and Welwitschia remain embedded in 

 the tissue of the gametophyte, they 

 apparently absorb nourishment more or 

 less throughout their entire surfaces, the 

 cotyledon remaining indistinguishable as 

 a definite organ. As soon, however, 

 as the stem and root begin to leave 

 this tissue the growth of the cotyle- 

 don is rapid and it quickly assumes 

 proportions commensurate with its func- 

 tions. From this example afforded by 

 the embryos of Gnetum and Welwitschia, 

 we might conclude that the cotyledons 

 of Conifer embryos are never called upon 

 to function and hence never develop. 



