EXTRAFLORAL NECTARIES. 29 



honey -loving insects through which cross-fertilization is secured. 

 It does not appear, however, that the floral nectaries of the cotton 

 have any connection with the problem of weevil resistance, although 

 the weevils seem in Guatemala to spend a considerable part of their 

 time in the floAvers, which are indeed the only safe places for them 

 on plants protected by the keleps. It had been noticed from the first 

 that the keleps seldom visit the cotton flowers, and Mr. Kinsler has 

 learned a very adequate explanation of this fact, namely, that they 

 are able to climb out of the flowers only with considerable difficulty. 

 and sometimes remain imprisoned in spite of all their efforts to 

 escape. 



The functions of the extrafloral nectaries of plants are, as far as 

 can be ascertained, similar to those of the floral nectaries to the extent 

 that they attract insects, but beyond this there is a fundamental dif- 

 ference; the floral nectaries and highly colored floral organs serve to 

 secure visits of flying insects and thus maintain intercommunication 

 and cross-fertilization between the different members of the same 

 species, in spite of the fact that the individual plants are rooted fast 

 in the ground. The extrafloral nectaries, on the other hand, attract 

 to the plants insects which will remain upon them as permanent resi- 

 dents, and this is the end secured by the extrafloral nectaries of the 

 cotton. 



It may be objected by some that no use or benefit to the plant lias 

 been ascertained in the case of many species which have extrafloral 

 nectaries and other insect-attracting devices. Much remains to be 

 learned concerning these marvelous biological specializations, and 

 there are two obvious alternatives which need to be canvassed before 

 belief in the adaptive nature of extrafloral nectaries and analogous 

 structures can be destroyed. The character and extent of many such 

 specializations show that they have existed for a long time. They 

 may have served protective purposes no longer apparent. The other 

 consideration is that some of the symbiotic specializations existing 

 between such plants as Cecropia and Acacia and their insect inhab- 

 itants have arisen through selective encouragement, much as the 

 special characters of our domestic plants and animals have been 

 developed. It may be sufficient, in other words, that the nectaries or 

 other structures be of use to the insects which have done the selecting. 

 It may seem absurd to think of bushes or trees as having been domesti- 

 cated by ants many thousands of years ago. but the wonder is no 

 greater than that ants and termites regularly maintained subter- 

 ranean fungus gardens ages before mushroom culture was undertaken 

 by man. 



