124 VIOLA TRICOLOK. 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 (Bhingfa rostrata) 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 tune 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 of these bees doing so. H. Muller 



apparently did not suck the nee- has also seen the hive-bee at work, 



tar, but was attracted by the pa- but only on the wild small- 



pillse which surround the stigma. flowered form. He gives a list 



H. Muller also saw a small bee, au (' Nature,' 1873, p. 45) of all the 



Andrena, which could not reach insects which he has seen visiting 



the nectar, repeatedly inserting both the large and small-flowered 



its proboscis beneath the stigma, forms. From his account, I sus- 



where the papillae are situated ; pect that the flowers of plants in 



so that these papillae must be in a state of nature are visited more 



some way attractive to insects. A frequently by insects than those 



writer asserts ( ' Zoologist,' vol. of the cultivated varieties. He 



iii.-iv. p. 1225) that a moth has seen several butterflies suck- 



(Plusia) frequently visits the ing the flowers of wild plants, 



flowers of the pansy. Hive-bees and this I have never observed in 



do not ordinarily visit them, but gardens, though I have watched 



a case has been recorded (' Gar- the flowers during many years, 

 deners' Clrouicle,' 1844, p. 374) 



