THE FLOWER 119 



anthers are pressed against the end of the style. The 

 pollen grains are few and unusually small. Fertilization 

 is effected in the closed flowers, and abuudant seed results, 

 the pods seeding far more freely indeed than those of the 

 ordinary flowers. In some species of Violet, these cleistog- 

 amous flowers are concealed under the leaves, or are borne 

 on runners underground. 



232. Self-fertilization prevented. — Many flowers are 

 habitually fertilized either (1) by their own, or (2) by 

 foreign pollen, — sometimes in one way, sometimes in the 

 other, as chance decides. In the great majority of flower- 

 ing plants, however, cross-fertilization is the rule. Self- 

 fertilization may be absolutely prevented. Tliis must be 

 the case when the flower bears only pistils (is pistillate^, 

 or stamens (is staminate). Sometimes the staminate and 

 pistillate flowers are produced on separate individual plants 

 (when the plants are said to be dioecious^ ; sometimes on 

 the same plant (when the species is monoecious). An 

 equally sure mode of preventing self-fertilization is seen 

 where the pistils and stamens, though both present, are 

 active at different times. This may well be illustrated 

 by the common Plantain. , The flowers are borne on long 

 spikes. The unfolding of the flowers '' proceeds from 

 base to apex of the spike in regular order, and rather 

 slowly. While the anthers are still in the unopened 

 corolla and on short filaments, the long and slender hairy 

 stigma projects from the tip and is receiving pollen blown 

 to it from neighboring plants or spikes : a day or two after- 

 wards, the corolla opens, the filaments greatly lengthen, 

 and the four anthers now pendent from them give their 

 light pollen to the wind ; but the stigmas of that flower 

 and of all below it on that spike are withered or past 

 receiving pollen."^ 



233. When the stamens mature first, as in many flowers, 

 the condition is termed proterandry. In the opposite case, 

 proterogyny, which is less usual, the pistils have been fertil- 

 ized or are no longer receptive by the time the anthers open. 



1 Asa Gray, " Structural Botany," p. 219. 



