DEVELOPMENT OF PLANTS 373 



pro-embryo of Cycas (Fig. 248, A). In this connection it should 

 be noticed that only a portion of the gametospore, as in the 

 cycads, is used in forming the embryo. In all the preceding 

 groups, as the mosses, ferns, etc., the gametospore in germinating 

 behaves as an ordinary cell, dividing into two cells which con- 

 tinue the process. In the Pinales the larger portion of the 

 gametospore serves as a storehouse for food, cell formation being 

 confined to the upper end of it (Fig. 255, B, C). With one ex- 

 ception this is the only group characterized by this peculiar ger- 

 mination which is more suggestive of the growth of the animal 

 egg where a large portion of the egg is reserve food for the nourish- 

 ment of the embryo. The nourishment of the female gamete 

 by the jacket cells is also suggestive of certain animals in which 

 the egg cells are formed in a similar manner. The embryo is 

 developed from the uppermost plate of cells which are pushed into 

 the cells of the gametophyte by the elongation of the suspensory 

 cells just below them (Fig. 255, E). Each of these four cells 

 may form an embryo (Fig. 256, 2) or they function collectively 

 in this growth. The result is the same in all cases, rarely more 

 than one embryo being found in a seed. The mature embryo 

 consists of a stem bearing two or several laterally-placed coty- 

 ledons and a root with root cap (Fig. 256, 3). Attending this 

 formation of the embryo, pronounced changes occur in the 

 sporangium. It steadily increases in size and the integuments 

 become modified into a hard coat, or the outer layer may be 

 pulpy, as in some of the cycads. The gametophyte also increases 

 in size, and as the embryo matures it absorbs all the tissues of the 

 sporangium, thus filling the space within the integument (Fig. 

 257). The cells of the female gametophyte are often called the 

 "endosperm." By these growths the seed is formed and pre- 

 pared for its dormant state, as in the preceding order. In some 

 cases the integument forms a membranous outgrowth, which 

 assists in the distribution of the seeds (Fig. 258, Q. It is inter- 

 esting to note that the seeds are so attached to these wings that 

 they rotate in falling to the ground, thus retarding their fall and 

 making possible a wider flight. The stimulus resulting from the 

 fusion of the gametes also produces extensive changes outside of 



