398 



SEED AND FRUIT OF ANGIOSPERMS 



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 megasporoph^^U behaves in this way and opens by 

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



f 



Fig. 276. Seed structure: A, section of a nearly mature seed of Lepid- 

 ium. The stem of the embryo is differentiated below into a hypocotyl, hy^ 

 and above into an epicotyl, pi, commonly known in the seed as the plumule, 

 r, root with root cap; c, the two cotyledons, which are bent over, lying one 

 upon the other; v, vascular bundles extending through the stem into the 

 cotyledons, where they form a network of veins; en, remains of endosperm. 

 B, section of seed of water lily (after Conard) — e, embryo, surrounded by a 

 layer of endosperm cells; mg, cells of the megasporangium; i, integument. 



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 



