DEVELOPMENT OF PLANTS 381 



sac (Fig. 275, A). The first division of the gametospore is trans- 

 verse, resulting in the formation of an outer cell, i. e., facing the 

 micropyle, and an inner daughter cell. The outer cell divides 

 several times, usually in the same plane, forming a row of cells 

 (known as the suspensor) which pushes the inner daughter cell 

 (called the embryo cell) into the cavity of the embryo sac. The 

 suspensor and embryo cell constitute the pro-embryo (Fig. 275, 

 B). The synergids, which are partly consumed during the en- 

 trance of the tube cells and the process of fertilization, usually 

 become entirely disorganized and absorbed during these early 

 stages of germination. The embryo is formed by the repeated 

 divisions of the embryo cell of the pro-embryo, assisted to a 

 varying extent by one or more of the adjoining cells of the sus- 

 pensor (Fig. 275, C-F). The remaining cells of the suspensor 

 are ultimately disorganized or they may increase greatly in size 

 and themselves become the principal means of absorbing food and 

 transferring it to the embryo. The structure of the mature 

 embryo varies greatly. In some genera, as in the orchids, Indian 

 pipe, etc., it remains rudimentary, consisting of only a few cells. 

 Among the monocotyledons, the embryo cell frequently produces 

 the single cotyledon, while the next underlying cell of the sus- 

 pensor forms the root and the laterally-placed growing point of 

 the stem (Fig. 279). The pro-embryo of dicotyledons is fre- 

 quently a filament of cells of varying length and the embryo 

 cell, by a regular series of divisions, gives rise to the stem, two 

 laterally-placed cotyledons and all of the root, save the tip, which 

 is formed from the cells adjoining the embryo cell (Fig. 276, A). 

 128. The Fruit and Seed. — Various changes occur in the 

 sporangium during the growth of the embryo. More frequently, 

 perhaps, the embryo sac enlarges, absorbing all the cells within 

 the integument, and it becomes filled with endosperm cells. In 

 a case like this, the embryo either remains small and embedded 

 in the endosperm (Fig. 279), or the embryo may entirely con- 

 sume the endosperm, the food in this case being stored in the 

 cotyledons (Fig. 276, A). Less commonly, the embryo sac ab- 

 sorbs only a portion of the sporangial tissue (often called the 

 perisperm) and consequently the embryo is associated with a 



