294 F. O, BOWER. 



consider the direction of the axis of the embryo as defined 

 by the position of the apical cells of stem and root, the foot 

 will here again appear as an outgrowth of tissues of the 

 hypocotyledonary axis. 



Thus we have a series of plants, starting with the Fili- 

 cineae, in which structures, to be regarded histologically as 

 outgrowths of the tissues of the hypocotyledonary axis (but 

 which cannot be themselves included under the morpho- 

 logical terms of stem, leaf, or root), perform the physio- 

 logical function of transfer of nutritive materials from the 

 prothallus (or endosperm) to the growing embryo. 



On comparing the orientation of these organs, i.e. their 

 relation to the other members borne on the axis of the 

 young plants, a want of uniformity will be found. In the 

 Fern the foot is on the opposite side of the axis to the coty- 

 ledon. In Isoetes the foot is on the same side of the axis 

 as the cotyledon. In Selaginella the foot is on the same 

 side of the axis as the first formed cotyledon, though, since 

 the two cotyledons appear almost simultaneously, too much 

 stress must not be laid upon the point. In Welwitschia it 

 has been shown that the feeder may appear on either side of 

 the hypocotyledonary axis, the choice being determined 

 according to the position of the seed during germination. 

 In Gnetum the orientation of the outgrowth, relatively to 

 the other members is not constant ; the point at which it 

 arises being also in this case determined according to the 

 position of the seed during germination. A case, such as 

 that of Gnetum, thus serves to throw light upon the want 

 of uniformity of orientation in the Ferns and Ligulatse ; as 

 these outgrowths may vary in orientation in different plants 

 of the same species, so also in various groups of plants the 

 orientation of the outgrowth may vary according to varying 

 conditions. 



Further, we find that as we rise in the scale, the time of 

 first appearance of these lateral outgrowths of the axis is 

 successively later. In the Fern the foot is recognisable in 

 very early stages of development of the embryo ; from the 

 constancy of its position, and of its origin in the true Ferns 

 from two definite octants resulting from the first divisions 

 of the oosphere, it has been regarded by some as being con- 

 nected in some fundamental way with those octants.^ 



In Selaginella the foot first makes its appearance at a 

 later stage of development of the embryo. In Welwitschia 



' This view I held myself when writing my former paper on the germina- 

 tion of Welwitschia. For reasons which will be obvious from what is here 

 written I have given up that opinion. 



