372 



HUTCHINSON'S POPULAR BOTANY 



(fig. 453, a). 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 (fig. 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 v 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 (Impatiens noli-me-tangere) 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 ; (b, c) stamens and pistil arranged for cross- 

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

 with the anthers of the shorter stamens. 



