THE WALLFLOWER 133 



while the plerome of the root is formed from the same 

 central group as that of the stem. 



We see, then, that the apex of the root is turned 

 towards the suspensor and the micropyle, as is always 

 the case in the embryos of flowering plants. The apex 

 of the stem is placed exactly at the opposite end of 

 the embryo. 



As growth proceeds, the embryo ceases to be 

 spherical. It first becomes flattened at the top and 

 then heart-shaped (see Fig. 47), forming two lateral 

 protrusions. These are the cotyledons (Fig. 46, D, and 

 47,, ct), the two first leaves of the embryo. The 

 growing point of the stem lies between them (g.p). 

 The class to which the Wallflower belongs derives 

 its name, Dicotyledons, from the fact that its embryo 

 always has two seed-leaves or cotyledons. The grow- 

 ing point of the embryonic stem in this class is 

 constantly terminal (i.e. in the middle line of the 

 embryo, at the end farthest from the micropyle), and 

 the two cotyledons lateral (i.e. one on each side of the 

 growing point). 



As the embryo attains its full size it gradually 

 occupies the whole of the curved embryo -sac, and 

 therefore of necessity becomes curved itself, so that 

 the cotyledons are bent back and lie parallel to the 

 young root or radicle. In- the Wallflower the coty- 

 ledons are so placed that their edges are turned 

 towards the radicle (see Fig. 49) ; in this case they are 

 said to be accumbent. This, however, is a character 

 of no great importance, as it varies in closely-allied 

 plants. 



