422 RELATION TO EN VIKONMENT. 



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

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

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

 stamens are absent and pistils pre ent the flower is pistillate. If 

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

 or neutral (snowbaU, marginal or showy flowers in h}'drangea). 

 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 imperject, or diclinous. Sometimes the impjerfect, or diclinouS; 

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

 cioiis (of one household). AMien staminate flowers are on cer- 

 tain individual plants, and the pistillate flowers of the same 

 species are on other individuals, the plant is dia-cioits (or of two 

 households). When some of the flowers of a jilant 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 weh-being 

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

 neutral flowers of certain species of hydrangea or viljurnum, the 

 showy petals serve to attract insects which aid in the polhnation 

 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 hvdrangea sometimes arc all neu- 

 tral and show\'. While such \'ariations sometimes contril)ute to 

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

 seed. In diclinous flowers cross ])ollination is necessitated. 



812. Form of the flower. — The flower as a whole has jorm. 

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

 individuals of a species arc of the same shape, though the\' may 

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

 ferent species are of the same t\pe as to form, so that often in Ihe 

 shape of the flower alone we can see the rclationshi]) of kind, 

 thougli the fornr of the llower is not llie most importani nor 

 always the sure inde.x of kinship. Since many flowers resemble 



