DEVELOPMENT OF PLANTS 383 



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 fruit, as in the fig, apple, 

 strawberry, etc., and in the pineapple, the axis of the inflores- 

 cence, as well as parts of the flower, become fleshy. These various 

 devices serve primarily to preserve the life of the embryo and 

 some of them also assist in distributing the seed. 



When conditions are favorable for growth, which may not be 

 till several years after the seeds have been scattered, the embryo 

 renews its growth. The region below the cotyledons, the hypo- 

 cotyl, or base of the cotyledon itself, elongates and pushes out 

 the root which growls down into the soil, and by a later growth 

 the stem tip, with or without the cotyledons which may remain 

 in the seed, elongates and develops the characteristic stem, 

 branches, leaves and sporophylls of the parent plant. The struc- 

 ture and variations of the mature sporophyte have been presented 

 in the first part of the work, pages 7-138, and will be further 

 considered in the following studies. The terms sporangium, 

 microsporophyll and megasporophyll have been retained up to 

 this point in the work in order to keep clearly before you the 

 progress and relationship of the variations that have attended the 

 evolution of plant life. Now that we have arrived at the highest 



