422 RELATION TO ENVIRONMENT. 



etc. Flowers which lack both floral envelopes are naked. When 

 pistils are absent but stamens are present the flowers are stami- 

 nate, whether floral envelopes are present or not; and so when 

 stamens are absent and pistils present the flower is pistillate. If 

 both stamens and pistils are absent the flower is said to be sterile 

 or neutral (snowball, marginal or showy flowers in hydrangea). 

 Flowers with both stamens and pistils, whether or not they have 

 floral envelopes, are perfect (or hermaphrodite),' so if only one 

 of these sets of essential organs of the flower is present the flower 

 is imperfect, or diclinous. Sometimes the imperfect, or diclinous, 

 flowers are on the same plant, and the plant is said to be monoe- 

 cious (of one household). When staminate flowers are on cer- 

 tain individual plants, and the pistillate flowers of the same 

 species are on other individuals, the plant is dioecious (or of two 

 households). When some of the flowers of a plant are diclinous 

 and others are perfect, they are said to be polygamous. 



Many of these variations relating to the presence or absence of 

 flower parts in one way or another contribute to the well-being 

 of the plant. Some indicate a division of labor; thus in the 

 neutral flowers of certain species of hydrangea or viburnum, the 

 showy petals serve to attract insects which aid in the pollination 

 of the fertile flowers. It must not be understood, however, that all 

 variations in plants which results in new or different forms of flowers 

 is for the good of the species. For example, under cultivation 

 the flowers of viburnum and hydrangea sometimes are all neu- 

 tral and showy. While such variations sometimes contribute to 

 the happiness of man, the plant has lost the power of developing 

 seed. In diclinous flowers cross pollination is necessitated. 



812. Form of the flower. The flower as a whole has form. 

 This is so characteristic that in general all flowers of the different 

 individuals of a species are of the same shape, though they may 

 vary in size. In general, flowers of closely related plants of dif- 

 ferent species are of the same type as to form, so that often in the 

 shape of the flower alone we can see the relationship of kind, 

 though the form of the flower is not the most important nor 

 always the sure index of' kinship. Since many flowers resemble 



