38 WEEVIL-RESISTING ADAPTATIONS OE COTTON. 



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far studied in the extent to which the bracts are grown together at 

 the base. Sometimes they are united for a quarter or even a third 

 of their length. (PL IV.' fig. 1, and PL X, fig. 1.) 



APPRESSED MARGINS OF BRACTS. 



In both of these Guatemalan varieties the margins of the bracts of 

 young involucres are firmly and closely appressed, in striking con- 

 trast with the Sea Island and Egyptian varieties, where the bud is 

 commonly exposed even when very young. This form of protection 

 is effective while it lasts, but in the Rabinal cotton the involucre is 

 too small, and the growth of the young bud soon separates the bracts 

 and permits the entrance of the weevil. The United States Upland 

 varieties are intermediate between the Sea Island and the Kekchi cot- 

 tons in the degree to which the iirvolucres are closed and the margins 

 fitted together. A large proportion of the Upland involucres give 

 ready access to the weevils, while most of those of the Kekchi cotton 

 remain effectively closed for a longer period, as will be understood 

 after a survey of the other involucral characters which conduce to 

 the same result. 



In one respect the firmly closed involucres of the Rabinal cotton 

 seemed almost like an advantage to the weevil rather than the con- 

 trary, for the insect is not admitted to the bud until it is about large 

 enough to furnish a place of development for a larva. The plant 

 having taken control, as it were, of this relation, the weevils have not 

 needed to possess an instinct against the destruction of young buds. 

 Those of the open involucrecl Sea Island varieties often were attacked 

 while still altogether too small to bring a larva to maturity. The 

 advantage of the closed involucres lies, no doubt, in the fact that they 

 shorten the period of access and allow some of the buds to escape 

 which would be punctured either for feeding or for egg laying if the 

 weevil has a longer opportunity. (PL IV.) 



The Rabinal cotton culture is that in which the plants are cut 

 back yearly to the ground. During the next month, or until the buds 

 begin to develop on the new shoots, the weevils have no, breeding 

 places and nothing to feed upon except the leaves and leaf buds. In 

 patches where the weevils are abundant the leaf buds are eaten out 

 so persistently as to seriously interfere with the growth of the plants, 

 and the very young flower buds were also reached in some instances 

 by boring through the involucres. When attacked at this stage the 

 buds wither and drop off. They serve the weevils only for feeding 

 purposes, and their use in this way only postpones the time when 

 breeding can be resumed. 



The cotton at Rabinal was often overrun by two species of small 

 black ants, identified by Dr. W. H. Ashmead as belonging to the 



