28 WEEVIL-RESISTING ADAPTATIONS OF COTTON. 



the later and more upright varieties the flowers are not formed until 

 the wood of the branches has hardened and become strong and rigid. 

 Pendent bolls may thus be said to be incompatible with the cluster 

 habit, which is brought about by the abnormal shortening and thick- 

 ening of the lateral branches, which are able to hold their flowers and 

 fruits rigidly upright, except as they may be turned sidewise by being 

 crowded together. The cluster cottons, too. have the undesirable 

 tendency to an abnormal multiplication of squares and young bolls, 

 many more than the restricted leaf surface of the plant will enable 

 it to ripen. This superabundance of flowers and fruits gives, how- 

 ever, the greater encouragement to the weevil, and uses up vegetative 

 energy which could be better employed in the prompt ripening of the 

 bolls already set. It is no uncommon thing, however, for even half- 

 sized bolls of cluster cottons to die without any sign of external 

 injury or disease, while other varieties close by remain perfectly 

 healthy. The cause is probably to be found in inadequate nutrition, 

 but this might also be expected to give them increased susceptibility 

 to injur} 7 from parasitic enemies of every kind. 



It is not unlikely, too, that the drooping habit may be connected 

 with the greater size of the inside nectaries of the Guatemalan vari- 

 ety. These :tre, as far as we have seen, larger than in any other 

 American variety yet known ; but the Asiatic cottons, which have the 

 inside nectaries still larger and more active, are also more definitely 

 pendent. The involucre is grown together at the base, as though to 

 more thoroughly protect the nectaries from above — from the sun, 

 which would dry up the secretion, and from the rain, which would 

 wash it off. 



The nectar is formed in great abundance, and Mr. F. J. Tyler, of 

 this Department, has called attention to the fact that the surface of 

 the nectaries of the Asiatic cottons, instead of being merely papil- 

 late, as in the American Upland varieties, has a covering of close- 

 standing fine hairs, to which its velvety appearance is due. 



Finally, it may be remarked that for cotton with upright bolls the 

 inside nectaries are often an element of danger, since when the secre- 

 tion is abundant and is not removed it flows along the bases of the 

 involucre and may serve as a medium for the germination of parasitic 

 fungi or bacteria. Bolls are not infrequently found diseased around 

 the base, apparently from this cause. 



EXTRAFLORAL NECTARIES. 



The cotton plant is not without floral nectaries similar to those of 

 related genera, consisting of fringes of nectar-secreting hairs lining 

 the pits inclosed between the bases of the petals. The nectar serves. 

 doubtless, the same purpose as in other plants, the attraction of the 



