436 



BOTANY 



The four cells of one of the uppermost tiers elongate into four long 

 tubes, and push the cells destined to become the rudiments of an 

 embryo deep into the tissue of the prothallium. From these, by- 

 further division, either a single embryo arises or, by the longitudinal 

 division of the embryonic rudiment, four embryos are formed, only 



7~el 



mM 



it 



msF 



n 



Fig. 368.— Picea vulgaris. A, Egg-cell with nucleus (on) and ventral canal-cell (el) ; B, egg-cell in 

 process of fertilisation ; on, nucleus of egg ; sn, the male nucleus which has passed from the 

 pollen-tube (p) into the egg-cell ; 0, later stage, showing the two nuclei in process of fusion ; 

 D, lower part of egg, showing two of the four nuclei ; E, F, successive stages, resulting injthe 

 formation of four rows of cells (two only visible) arranged in tiers ; G, the cells of the middle 

 tier have elongated and pushed the lower tier of cells, which have undergone division,~_into 

 the endosperm, (x 90.) 



one of which, however, attains its full development. Even when 

 several archegonia are fertilised, as is usually the case, the mature seed 

 contains only one embryo, by which, in the course of its growth, the 

 rudiments of all the other embryos have been supplanted. 



The embryo of the ripe seed is provided with two or several 



