THE WHITE LILY 



189 



e.s. 



is a lateral structure. The group marked r forms the 

 hypocotyl and root, and also contributes something to 

 the suspensor. 



The form of the more advanced embryo, after a 

 great many cell-divisions have taken place, is shown 

 in Fig. 91. Towards the top of this figure we see 

 the radicle (r), with its growing point directed towards 

 the micropyle (m). 

 On one side of the 

 embryo is a depres- 

 sion, in which the 

 lateral growing point 

 of the stem (g.p.) is 

 situated. All the 

 part beyond this is 

 the cotyledon (c), 

 which at this stage 

 occupies more than 

 half the entire length 

 of the embryo. 



The essential dif- 

 ferences, then, be- 

 tween the embryo FIG. 89. Very young embryo of A lisma 

 Of a Monocotyledon Pkntago, a Monocotyledon n , cells 



-, ,, -r^ 7 . of nucellus ; e.s, membrane of embryo- 



ana tnat 01 a JJlCOty- gac> ^he embryo with its suspensor 

 ledon are these. In consists of three cells, the basal cell 



the Monocotyledon ein g. 7 lar s e - Magnified about 



. < 500 diameters, 



there is a single ter- 

 minal cotyledon, and the apex of the stem is lateral, 

 while in the Dicotyledon there are two lateral cotyle- 

 dons, with the terminal apex of the stem between them. 

 These distinctions are on the whole constant, in spite 

 of great variations in the embryology of both Classes. 



The dimensions of the embryo in the Lily, as com- 

 pared with the whole seed when ripe, are shown in 

 Fig. 91. At the stage figured the chief systems of 

 tissue in the young plant are already marked out. The 



