39^ A TEXT-BOOK OF BOTANY. 



some plants produce cleistogamous or closed flowers. In these 

 flowers the corolla is usually suppressed. The flowers develop 

 stamens and pistils but remain closed, and thus there is no chance 

 for cross-pollination. The cleistogamous flowers appear later 

 than the regular flowers and are more or less inconspicuous, 

 developing under the leaves and sometimes underground. Of the 

 plants producing cleistogamous flowers, the following may be 

 mentioned : various species of Viola, Polygala, etc. 



Classes of Flowers. — As we have seen, the megasporophylls 

 and microsporophylls in the Gymnosperms are borne on separate 

 branches, thus giving rise to two kinds of flowers or cones. While 

 the separation of the stamens and pistils is exemplified in a 

 number of plants in the Angiosperms, still it is not the rule, 

 and these two elements are usually borne close together on the 

 same axis, — i.e., they both enter into a single flower structure. 

 Such a flower is said to be hermaphrodite or bisexual, and most 

 of the conspicuous flowers are of this kind, as roses, buttercups, 

 lilies, etc. Inasmuch as the stamens and pistils constitute the essen- 

 tial elements of the flower, hermaphrodite flowers are also spoken 

 of as PERFECT, providing the stamens and pistils are capable of 

 exercising their generative functions. When the stamens and 

 pistils occur in separate flowers the flowers are said to be uni- 

 sexual or IMPERFECT, as in willow, oak, hickory, etc. A flower 

 having only a pistil or pistils is called pistillate (Fig. 219, 

 A), while one having only a stamen or stamens is staminate, as in 

 oaks. The staminate and pistillate flowers may be borne on the 

 same plant, when it is said to be moxcecious, as in castor bean, 

 chestnut, hickory, alder ; or they may be borne on separate plants, 

 when the plant is called dicecious, as in willows and poplars. 

 Plants bearing hermaphrodite and unisexual flowers on the same 

 individual plant or on different individuals are called polygamous, 

 as in Ailanthus. 



A COMPLETE flower is one which possesses both kinds of essen- 

 tial elements and both kinds of floral envelopes, and is symmet- 

 rical when a plane can be laid in all directions, the parts being 

 alike, and when the number of parts in each circle is the same or 

 when the n-umber in one circle is a multiple of that in the others ; 

 as a rule, the number of stamens is some multiple of one of the 



