DEVELOPMENT OF PLANTS 397 



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 under- 

 lying cell of the suspensor forms the root and the laterally-placed 

 growing point of the stem (Fig. 279). The pro-embryo of dico- 

 tyledons is frequently 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 

 varying amount of endosperm, which in turn is surrounded with 

 sporangial cells or perisperm, as in the water lily (Fig. 276, B). 

 The integument usually undergoes pronounced changes during 

 this growth, becoming hard and tough to protect the parts within, 

 and often developing appendages of various kinds, as hairs and 

 wings, to promote the distribution of the seed (see gymnosperms, 

 page 374). 



The stimulus of fertilization extends beyond the changes 

 wrought in the sporangium. This is particularly noticeable in 

 the megasporophyll and often in adjacent parts which keep pace 

 with the growth of the sporangium and often undergo remarkable 

 transformations. The result of this total growth is called the 

 fruit, while the term seed is restricted to the modified sporangium 

 with its integument and embryo. The megasporophyll may form 

 a firm coat that is closely attached to the seed, as in the corn and 



