The Orderly Cycles Pursued in Growth 



353 



the accompanying picture (figure 134). The reader will recall 

 that the egg-cell is the female reproductive cell formed inside the 

 embryo-sac within the ovule, and that it needs to be fertilized by 

 a male cell brought by a pollen-tube, before it can develop to an 

 embryo. Immediately after fertilization, the egg-cell divides into 

 two; these grow in size, and again divide, and so on in a way to 



Fig. 134. — Typical stages in the development of an egg-cell into an enil^iyo (of Rape). 

 The original egg-cell lay at the bottom of the embrj'o sac of which a part is shown in 

 the figure on the left, while the other figures show the development of the initial cell, 

 at the top of the suspen.sor, into the embryo. (Adapted from pictures on a wall-chart 

 by L. Kny.) 



produce a line of cells forming a structure called a suspensor, 

 which carries a terminal, or initial, cell out into the middle of the 

 embryo-sac, where there is ample space for the development of 

 the forthcoming embryo. Then the initial cell begins to divide, 

 first at right angles to the earlier divisions, then again and again 

 in other planes with great regularity, as represented in our pic- 

 tures, until finally a many-celled ball is produced. Then the 

 regularity ceases, and cell division becomes more active at two 



