316 CLEISTOGAMIC FLOWERS. CHAP. VIIL 



error, though only a small proportion of them do so. 

 This appears to depend in some cases on their anthers 

 not containing even a trace of pollen, but more gene- 

 rally on bees not visiting the flowers. I twice covered 

 with a net a group of flowers, and marked with threads 

 twelve of them which had not as yet expanded. This 

 precaution is necessary, for though as a general rule 

 the perfect flowers appear considerably before the 

 cleistogamic ones, yet occasionally some of the latter 

 are produced early in the season, and their capsules 

 might readily be mistaken for those produced by the 

 perfect flowers. Not one of the twelve marked perfect 

 flowers yielded a capsule, whilst others under the net 

 which had been artificially fertilised produced five 

 capsules ; and these contained exactly the same aver- 

 age number of seeds as some capsules from flowers 

 outside the net which had been fertilised by bees. I 

 have repeatedly seen Bonibii-s hortorum, lapidarius, and 

 a third species, as well as hive-bees, sucking the 

 flowers of this violet : I marked six which were thus 

 visited, and four of them produced fine capsules ; the 

 two others were gnawed off by some animal. I 

 watched Bonibus hortorum fo'r some time, and when- 

 ever it came to a flower which did not stand in a con- 

 venient position to be sucked, it bit a hole through the 

 spur-like nectary. Such ill-placed flowers would not 

 yield any seed or leave descendants ; and the plants 

 bearing them would thus tend to be eliminated through 

 natural selection. 



The seeds produced by the cleistogamic and perfect 

 flowers do not differ in apparance or number. On 

 two occasions I fertilised several perfect flowers with 

 pollen from other individuals, and afterwards marked 

 some cleistogamic flowers on the same plants ; and the 

 result was that 14 capsules produced by the perfect 



