THE STRUCTURE OF THE FLOWER 325 



egg-cell. The next generation may be said to begin with the 

 fertilised egg-cell, which develops into a plant embryo. 



The form of the embryo, at the stage when it is ready to 

 begin independent life, may be seen by examining a ripe pea. 

 Within the seed-coat we find two thick, whitish bodies, which 

 occupy nearly the whole of the interior and are known as the 

 cotyledons. Between them we can see a tiny root (the radicle), 

 and a bud which will form the leafy shoot {the plumule). The 

 cotyledons are really the two first leaves of the young plant, 

 which have given up the usual form and appearance of leaves 

 in order to act as storehouses of food material for the young 

 plant to draw upon before it has expanded its green leaves and 

 can nourish itself independently. 



In other cases, such as the wheat and the coffee-bean, the 

 embryo does not occupy the whole interior of the seed, but lies 

 more or less embedded in a store of food material which is 

 known as the endosperm. The cotyledons do not in these cases 

 store the food themselves, but they have the power of sucking 

 it out of the endosperm. 



The Flowering Plants are divided into two main groups, the 

 Dicotyledons and Monocotyledons, according as their seedlings 

 have two seed leaves, or only one. These two groups also differ 

 in floral characters. For instance, the dicotyledonous flower 

 has, as a rule, four or five parts in each whorl, and the perianth 

 is often differentiated into calyx and corolla, while the 

 monocotyledonous flower has its parts in threes, and the 

 perianth is undifferentiated. 



We must now return to our description of flower structure, 

 and consider some of the chief modifications which the 

 general type may undergo. A typical flower contains 

 both gynaeceum and andrcecium, and is called hermaphrodite. 

 But it is possible to have unisexual flowers, which may be 

 either wholly male, or wholly female. This is brought about 

 by the suppression either of the gynaeceum or andrcecium 



