332 EEPORT UPON COTTON INSECTS. 



eggs, than good in drawing the enemies of their larves; and, this being 

 the case, natural selection ought to remove the power of secretion. 

 But a moment's reflection will show us that natural selection cannot for 

 this reasom remove the glands or their activity. For a long time the 

 cotton plant has been subjected to the methodical selection of man, 

 who, in selecting seed to sow, pays no attention to the presence or 

 absence of active nectar glands on the parent plant, but seeks to pro- 

 duce prolific plants of vigorous growth and good staple; so that no 

 peculiarity which does not tend directly to lessen the vital force of the 

 plant, and thus bring itself directly into conflict with the purpose ot" 

 man's selection, can be removed by natural selection. But if, under 

 the same circumstances, the production of this nectar is a direct drain 

 on the vital force of the plant, a very different result must follow ; for 

 the methodical selection of man then becomes a factor in the broader 

 selection of nature, and tends to the extinction of those varieties which, 

 owing to their greater secretion of nectar, were even a little less vigor- 

 ous or less prolific than their fellows which chanced to secrete less, so 

 that the result must inevitably be the partial or total absence of nectar 

 in the most vigorous and prolific varieties. My observation has shown 

 me that there is not a whit less nectar secreted by the glands on the 

 finest "Dixon-cluster" stalk than by those of the poorest scrub; from 

 which I infer that the production of nectar causes very little drain on 

 the energy of the plant aside from the mere vital force which must pre- 

 side over every physiological act. This, I think, goes to show the 

 correctness of Darwin's idea that all nectar was at first merely an 

 excretion; and also that the material used in the elaboration of nectar 

 by large, specialized, and active glands which serve other than excretory 

 purposes is of such a nature that it can readily be spared by the plant 

 without any impairment of its vigor.* 



But if the glands of the cotton plant seem to have been produced to 

 secure the protection of the leaves and flowers of the plant from leaf 

 or petal eating insects like ants, those of the cow-pea seem designed to 

 protect the flowers and especially the young fruit from all insects, but 

 chiefly from such fruit-eating larvae as those of Heliothis. 



While watching Viciasativa, Darwin, found that hive bees, while visit- 

 ing the stipular glands, "never even looked at the flowers which were 

 open at the same time ; whilst two species of humble-bees neglected the 

 stipules and visited only the flowers."t About 10 a. in. one day in August, 

 while the sun was shining brightly, I noticed that several humble-bees, 



* This, I think, explains the Tact that the glands of Pteriz aquilina still secrete 

 while the frond is young, though they are not needed for its protection against any 

 insect, as discovered by Francis Darwin. They were probahly developed centuries 

 ago, when the young fronds may have experienced the most urgent need of protection, 

 from some leaf-eating animal, and, causing little drain on the vitality of the plant, 

 are still retained, though in some, perhaps all, parts of the world they are no longer 

 of use. 



t Cross and Self Fertilization, 1877, p. 403, note. 



