372 



HUTCHINSOX'S POPULAR BOTANY 



(fig. 453, ). They are met with in dry and sandy fields during the sultry 

 months of July and August : but few probably have noticed, earlier in 

 the year, the small bud-like unexpanded flowers of this plant ifig. 453, 6). 

 These are cleistogamic flowers, which never open undeveloped flower- 

 buds, with anthers and stigmas that mature so that perfect fruits are pro- 

 duced. "Were you to open one of these buds at the moment of pollination 



(fig. 453, c). you would find 

 that the long and flexible 

 style (st) had curled round 

 so as to bring the inner side 

 of its forked stigma in con- 

 tact with one of the anthers. 

 Perhaps you would even 

 find that the anthers had not 

 opened, but that the pollen- 

 tubes had perforated its 

 delicate walls and were 

 growing in the direction of 

 the stigma. 



The Dog-violet (Viola 

 canina) is another plant 

 which produces these un- 

 developed flowers. Pro- 

 fessor Ainsworth Davis re- 

 marks that " in summer the 

 ripe fruit of the cross- 

 pollinated flowers will be 

 found, and, close to them, 

 minute bud-like structures. 

 These are the cleistogamic 

 flowers : their anthers are so 

 placed that the pollen-grains 

 can send their tubes straight 

 to the stigma. Such a 

 flower produces, perhaps, 

 only two hundred pollen- 

 grains, as opposed to some 

 thousands in an ordinary blossom." As a rule, indeed, cleistogamic flowers 

 are pollen saving. Thus, a single self-pollinating flower of Wood-sorrel 

 (Oxalis acetosella) contains about four hundred grains : a flower of Touch- 

 me-not Balsam (I'mpatieiis noli-me-tangei'e) about two hundred and fifty : 

 and of Cut-grass (Leersia) not above fifty. Contrast these figures with 

 the number of pollen-grains in the Peony, 3,500,000, or in a single flower- 

 head of Dandelion. 365.000 ! 



FIG. 456. GREAT WILLOW-HERB (Epilobium hirsutum). 



(a) Flowering branch ; (6, c) stamens and pistil arranged for cross- 

 pollination. In (<f) the stigma-lobes have curled back to effect contact 

 with the anthers of the shorter stamens. 



