292 F. 0. BOWER. 



resembles other Gymiiosperms ; at the apex of the stem the 

 dermatogen is not well defined in young embryos, but in 

 the mature plant there is apparently a more independent 

 layer of dermatogen at the apex of the stem than is seen in 

 Ephedra. 



Soon after the cotyledons and apex of the root appear, 

 and after the procambium bundles are differentiated, the 

 feeder is formed by lateral outgrowths of the tissues of the 

 hypocotyledonary stem. Though it is no doubt the homo- 

 logue of the similar structure in "SYelwitschia, the two differ 

 from one another in certain details. The vascular bundles 

 of the hypocotyledonary stem, which in Welwitschia only 

 curve slightly outwards at the level of the feeder, describe 

 in Gnetum a strong curve, passing outwards along the 

 upper side of the organ nearly as far as its apex, then curv- 

 ing sharply, they return along its lower side. Thus the 

 arrangements for transfer of materials from the endosperm 

 are more elaborate in Gnetum than in Welwitschia. 

 Further, in Welwitschia, the seeds of which are fiat, and the 

 planes of the cotyledons parallel to that of the seed, I 

 have already shown ('Quart. Journ. Micr. Sci.,' Jan., 1881) 

 that the feeder may be formed at either of two points, the 

 choice being determined by the direction of gravity relatively 

 to the seed during germination. In Gnetum the seed is 

 polysymmetrical ; the direction of the planes of the cotyle- 

 dons, which are small, and not much flattened at an early 

 stage, bears no definite relation to the direction of gravity 

 during germination. The position of the feeder is, however, 

 determined by the latter, and the organ always appears on 

 the under side of the embryo as it lies during germination. 

 Hence it follows that the position of the feeder relatively to 

 the vascular system of the stem and to the position of the 

 cotyledons is inconstant in Gnetum, while in Welwitschia it 

 is constant. 



Comparing the seeds of the three genera of the Gnetacese 

 and their several modes of germination, it is seen that they 

 form a series in which the special adaptation for the transfer 

 of nutritive materials from the endosperm to the seedling 

 varies directly with the size of the seed, i. e. with the amount 

 of nutritive material to be transferred. In Ephedra the 

 endosperm is small, but still, in certain cases, the cotyledons 

 leave the endosperm before the store is used up, and the 

 further transfer has to be performed by the very inefficient 

 tissue of the suspensors. 



In Welwitschia the seed is larger, and, as before, the coty- 

 ledons leave the endosperm at a comparatively early stage ; 



