196 MORPHOLOGY OF ANGIOSPEEMS 



In 1STS Solms-Laubacli 15 stated that in Dioscoreaceae and 

 certain Commelinaceae the cotyledon is lateral in origin rather 

 than terminal. The stem-tip is terminal in origin, but is later 

 forced to one side by the strong growth of the cotyledon from 

 beneath. Such a departure is, of course, fundamental, but be- 

 fore any generalization is ventured it should be subjected to the 

 most critical investigation. Campbell 41 finds that in Zanni- 

 chellia the terminal cell of the proembryo gives rise to both coty- 

 ledon and stem-tip, the separation between the two organs being 

 determined by the first vertical division of the terminal cell 

 (Fig. 88). The same writer 47 has found another suggestive 

 variation in Lilaea subulata, one of the Juncaginaceae. The 

 embryonic root-tip, instead of being directed toward the sus- 

 pensor, is directed to one side, almost in continuation of the 

 axis of the stem-tip. This lateral origin of the root is regarded 

 by Campbell as a primitive feature, and suggestive to him of 

 Isoetes. In other particulars the embryo is of the Alisma type. 

 In this connection the recent results of Murbeck ° 5 with Ruppia 

 are suggestive. He confirms the account of Wille that a pri- 

 mary root is formed at the base of the embryo, but soon dis- 

 organizes, and that a lateral root, formed very early, is the first 

 functional one. This is very different from the account of 

 Ascherson in Engler and Prantl's " Die Xatiirlichen Pfianzen- 

 familien," which is followed in Goebel's " Organography," ac- 

 cording to which this lateral root is the primary root, its un- 

 usual position being due to displacement. 



DICOTYLEDONS 



The best-known dicotyledonous embryo is that of Capsella, 

 as described by Hanstein 7 and Famintzin, 17 and it has been 

 used as a basis of comparison ever since. To illustrate the 

 earlier stages in the development of the embryo, therefore, we 

 have made a rather complete scries of camera drawings from 

 sections of the embryo of Capsella (Figs. 89, 90; see also Fi<>\ 

 81). The proembryo is a filament of cells of varying length. 

 The apical cell divides first longitudinally, the next two divi- 

 sions being longitudinal and transverse in either order and 

 resulting in the octant stage. Whether the transverse division 

 precedes or follows the second longitudinal division, it sepa- 

 rates the cotyledonary and hypocotyledonary regions of the em- 



