124 



VIOLA TRICOLOR. 



Chap. IV. 



uncovered plant of the same variety, growing close by, produced 

 105 fine capsules. The few flowers which produce capsules when 

 insects are excluded, are perhaps fertilised by the curling inwards 

 of the petals as they wither, for by this means pollen- grains 

 adhering to the papillae might be inserted into the cavity of tha 

 stigma. But it is more probable that their fertilisation is effected. 

 as Mr. Bennett suggests, by Thrips and certain minute beetles 

 which haunt the flowers, and which cannot be excluded by any 

 net. Humble-bees are the usual fertilisers ; but I have more than 

 once seen flies (fihingia rostruta) at work, with the under sides of 

 their bodies, heads and legs dusted with pollen; and having 

 marked the flowers which they visited, I found them after a few 

 days fertilised.* It is curious for how long a time the flowers of 

 the heartsease and of some other plants may be watched without 

 an insect being seen to visit them. During the summer of 1841, 1 

 observed many times daily for more than a fortnight some large 

 clumps of heartsease growing in my garden, before I saw a single 

 humble-bee at work. During another summer I did the same, but 

 at last saw some dark-coloured humble-bees visiting on three suc- 

 cessive days almost every flower in several clumps ; and almost 

 all these flowers quickly withered and produced fine capsules. 

 I presume that a certain state of the atmosphere is necessary 

 for the secretion of nectar, and that as soon as this occurs the 

 insects discover the fact by the odour emitted, and immediately 

 frequent the flowers. 

 As the flowers require the aid of insects for their complete 



* I should add that this fly 

 apparently did not suck the nec- 

 tar, but was attracted by the pa- 

 pillae which surround the stigma. 

 H. Miiller also saw a small bee, an 

 Andiena, which could not reach 

 the nectar, repeatedly inserting 

 its proboscis beneath the stigma, 

 where the papillse are situated; 

 so that these papillae must be in 

 some way attractive to insects. A 

 writer asserts ( ' Zoologist,' vol. 

 iii.-iv. p. 1225) that a moth 

 (Plusia) frequently visits the 

 flowers of the pansy. Hive-bees 

 do not ordinarily visit them, but 

 a case has been recorded ('Gar- 

 deners' Ctrouicle,' 1814, p. 374) 



of these bees doing so. H. Miiller 

 has also seen the hive-bee at work, 

 but only on the wild small- 

 flowered form. He gives a list 

 (' Nature,' 1873, p. 45) of all the 

 insects which he has seen visiting 

 both the large and small-flowered 

 forms. From his account, I sus- 

 pect that the flowers of plants in 

 a state of nature are visited more 

 frequently by insects than those 

 of the cultivated varieties. He 

 has seen several butterflies suck- 

 ing the flowers of wild plants, 

 and this I have never observed in 

 gardens, though I have watched 

 the flowers during many years. 



