DEVELOPMENT OF PLANTS 365 



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 341). 



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 

 other grasses. Such a fruit is called a grain. Again the tough 

 walls of the megasporophyll are free from the seed, as in the 

 buttercup, forming a fruit known as the akene. The sporophylls 

 may become papery or hard and split open to scatter the seed. 

 Where a single megasporophyll behaves in this way and opens by 

 two valves, the fruit is called a pod or legume, example the bean, 

 or if by one valve the fruit is termed a follicle, example the 

 peony. Frequently wing-like processes develop from the mega- 

 sporophyll, as in the maple and ailanthus, which are of service in 

 distribution and in other ways, as in the manufacture of foods, 

 these organs often being green during the development of the 

 embryo. Such fruits are known as key fruits or samaras. In 

 other cases the sporophyll becomes fleshy, forming a berry as in 

 the currant or the inner layer forms a pit or stone, while the outer 

 layer forms the pulp and skin, as in the cherry and peach, fruits 

 known as drupes. In many fruits the receptacle becomes 

 fleshy and forms the major portion of the f^uit, as in the fig, 



