216 BOTANY FOR BEGINNERS CHAP. 



close up and never open again, but the anthers come in contact 

 with the stigma and self-pollination takes place. 



A very large number of plants produce two kinds of flowers 

 the ordinary open ones and minute closed ones. 



The small closed flowers, called Cleistogauiic flowers, are self- 

 pollinated and produce large quantities of seeds. The structure 

 and advantages of cleistogamic flowers must now be considered. 



The Structure of Cleistogamic Flowers. They are 

 very small and never open. The petals are rudimentary or 

 absent, the stamens few in number, the anthers small, the pollen 

 grains are few, producing their tubes while in the anthers, the 

 pistil is small, and the stigma almost absent. Pollination takes 

 place by the pollen tubes passing from the anthers down the 

 short style to the ovules in the ovary. 



Advantages of Cleistogainic Flowers. They seem to furnish 

 the following desirable results to the plant. 



1. They produce seeds in seasons when the ordinary flowers 

 which are insect-pollinated might be able, to produce none. 



2. They produce seeds with the smallest consumption of 

 matter, and the energy used is reduced to a minimum. The 

 amount of pollen used in the cleistogamic flowers of the Violet 

 is only the ^isVoo P art f t^* usec ^ by a Dandelion. Just 

 as many seeds being produced as in a perfect flower of the 

 Violet. 



3. They belong to plants which also produce zygomorphic 

 flowers which are pollinated by insects. But insects, in this 

 strange climate of ours, are very variable quantities. Hence 

 seasons might occur, and do occur, when the necessary insects 

 not being present no seeds would be formed but for the 

 cleistogamic flowers. 



Among the plants which produce cleistogamic flowers' are 

 the Wood-Sorrel, Violet, and Pansy. 



Fertilisation. When the pollen grains are deposited on 

 the stigma, they are generally held fast by its sticky surface. 

 The grains take up moisture and nutritive materials from the 

 stigma, and germination commences. Pollen tubes are pro- 

 duced, and these pass between the superficial cells of the stigma 

 and bore their way down the style. They feed, as they grow, 

 upon the tissue of the style, and enter the ovary. In the ovary 

 they find their way to the micropyles of the ovules. Each 



