Poly gal a polygama and P. pauciflora. 143 



different from others which bear cleistogamic flowers, or that 

 all these are merely teratological cases ? Hansgirg^ dwells 

 on the importance of light and other factors in determining 

 the development of blossoms, and states that flowers may- 

 be rendered potentially cleistogamic in several ways. Such a 

 condition he calls pseudocleistogamy and distinguishes varie- 

 ties according to the character. Kerner regards clcistogamy 

 as due primarily to lack of light. " This result throws some 

 light on the nature of the stimulus which causes the forma- 

 tion of the flowers in question. No open, aerial flowers were 

 produced by Viola sepmcola so long as it grew in the cool 

 shade of a dense wood, but when transferred to open ground, 

 accessible to sunlight, such flowers were developed. One can 

 hardly err in ascribing to the sun's rays a very important influ- 

 ence in stimulating plants to the inception of flowering shoots, 

 especially such as bear blossoms possessing bright colored 

 petals. Indirectly, however, this advantage accrues to the 

 plants in question that, living as they do in the deep shade, 

 where no bees would, in any case * visit them, even if they had 

 open flowers, they can confine their constructive energy to the 

 inception and development of cleistogamous flowers and save 

 themselves the trouble of producing open flowers adapted to 

 cross-pollination, but useless in the place in question. If the 

 spot where the violet grows becomes exposed to the sunlight 

 through the trees shading it being blown down or felled,, 

 humble and hive-bees make their appearance in search of 

 honey, and, buzzing from flower to flower, cross the flowers 

 one with another. In such circumstances the open, sweet- 

 scented violet blossoms are in request, and the same plant 

 individual, which for years in the dark shade has developed 

 none but cleistogamic flowers, is now stimulated by the sun's, 

 rays into producing flowers with expanded petals. 



^ Hansgirg. Bot. Central, 45, p. 74. 

 2 Natural Hist, of Plants, II, p. 395. 



