LIl] 



GXETUM 



463 



archegonia: in some species the megaspore contains numerous free 

 nuclei all of which are potentially sexual; after fertilisation a 

 sterile nutritive tissue, or endosperm, is formed in the lower part 

 of the spore. In Gnetum Gnemon the endosperm is often formed 

 before fertilisation. In the great reduction of the female apparatus 

 and in the nature of the endosperm Gnetum 1 agrees much more 

 closely with Welwitschia than with Ephedra. Attention has been 

 called to certain resemblances between the seed of Gnetum and 



- -a 



v 



FIG. 817. Seed of Gnetum africanum. a, outermost envelope; v, vascular strands; 

 b, outer integument; /, flange of micropylar tube; n, nucellar cap; c, inner 

 integument; p, endosperm. (After Mrs Thoday.) 



that of Bennettites 2 . For convenience of comparison a diagram- 

 matic section of a seed of Gnetum africanum is reproduced in 

 fig. 817. The outermost envelope, a, forms a green succulent 

 covering free to the apex ; the middle envelope, 6 (outer integument), 

 is free from the other envelopes except at the apex where it is 

 locked to the inner integument by the downward growth of a 

 flange,/, from the apical region of the inner integument; the inner 



1 Pearson (09); see also Karsten (92); (93 2 ); Lotsy (99). 



2 Berridge (11); (12); Thoday (Sykes) (11). 



