256 TRANS. ST. LOUIS ACAD. SCIENCE. 



of the bee are held in a similar way when the tender cellular tis- 

 sue is pierced with the tips of its maxillae. While many humble- 

 bees are addicted to boring the tubes of corollas, they also resort 

 to biting the tissues of the flowers by the aid of their mandibles. 



The opinion is current that perforated flowers are not as pro- 

 ductive as unperforated ones. Delpino has shown, in the case of 

 Symphytum tuberosum and Polygala Ghumcebuxus, that the perfo- 

 rated flowers are absolutely sterile. Ogle (98) states that many 

 flowers of Phaseolus multiflorus fail to produce seed because of 

 perforations. 



I doubt whether there are many flowers in which one can find 

 more perforations than in Symphytum officinale.* In stocks which 

 have several thousand flowers, hardly one can be found which is 

 not perforated. Several stocks in the Botanic Garden gave me 

 ample opportunity of seeing the results from perforated flowers. 

 I did not undertake to count the ripened fruits, but the greater 

 number of flowers developed some nutlets. At this time I had 

 not seen Loew's (63 6) experiments on this plant. His results 

 are so striking and conclusive that I give them somewhat in 

 detail. On the nth of June, 1885, he took several branches 

 which had passed anthesis. On these he had 73 flowers, and was 

 careful to remove later flowers ; on the 4th of August 46 flowers 

 were dry, while the remaining 27 flowers had matured 41 nut- 

 lets, so that 37 per cent, of the flowers were more or less fertile. 

 The full fertility of many plants, as Darwin has shown, depends 

 largely on cross-pollination. Insects do not commonly visit flow- 

 ers unless they get nectar or pollen in return, so that, when a 

 flower is constantly robbed, the regular pollinators do not receive 

 their due share of nectar or pollen, their visits are fewer, and con- 

 sequently there is less chance for cross-pollination. If the plant is 

 capable of self-pollination seeds may be developed, and often in 

 great abundance, yet Darwin has shown that the progeny of self- 

 fertilized flowers islcss vigorous than from cross-fertilized flowers. 

 If the structure of a flower is such that self-fertilization is prevent- 

 ed, and insects do not go to it in the I'egular way, sterility may 

 result. But in most of the flowers perforated there is an abun- 

 dance of nectar, and insects which perforate flowers are very 



• Xylocopa Virginica was frequently seen using longitudinal slits in the tube of the 

 corolla, but I did not succeed in seeing it make the perforations. 



