80 postelsia 



passes it on to the rest of the em- 

 bryo. The orientation of this feeder, 

 as Bower terms it, is not constant in 

 its relation to the other members of 

 the embryo. It always occurs just 

 above the transition plane between the 

 stem and the root, but its position on 

 the circumference of the embryo is 

 determined by the direction of gravity. 

 The seed of Welwitschia is more or 

 less flattened, and no matter which 

 side up it lies when germinating the 

 feeder is developed on the concave 

 surface of the embryo as the root 

 grows out and down into the soil. It 

 may then arise in either of two posi- 

 tions. The seed of Gnetwn is poly- 

 symmetrical and the planes of symmetry 

 of the embryo bear no definite rela- 

 tion to the direction of gravity during 

 germination. The feeder always arises 

 on the under side of the embryo and 



