PART I. — ORGANOGRAPHY. 



place only in one plane, and a chain or linear series of cells, 

 technically called the suspensor, ox pro-embryo, is formed. Then 

 the terminal member of this chain begins to divide in different 

 planes, forming a mass of cells. This latter is the real beginning 

 of the embryo, and, as cell-division proceeds, the mass gradually 

 becomes differentiated into the various organs of the embryo, a 

 rudimentary root, a rudimentary stem and rudimentary leaves 

 becoming recognizable. It is to be observed that the root end, 

 or radicle, always points toward the micropyle of the ovule. 



*K 



Fig. 298. 



Fig. 299. 



Figs. 298 to 301. — Diagrams representing 

 successive stages in the development of a dico- 

 tyledonous embryo, j in each case is the sus- 

 pensor or pro-embryo, and e, the embryo. In 

 Fig. 301, the embryo is so far advanced that the 

 first leaves, or cotyledons, c, c, may be recog- 

 nized; r, is the root, and a, the growing apex 

 of the stem. 



Fig. 301. 



While the embryo is forming, other important changes are 

 taking place in the embryo-sac. As soon as the oospore com- 

 mences its division, or sometimes even before that, the form- 

 ation of endosperm begins. The nucleus of the sac first divides 

 and, in some instances, forms a great mass of nuclei which 

 line the wall of the sac, as shown in Fig. 302. Afterwards, 

 these nuclei become perfect cells by the development of cell- 



