May 20. 1918 Chemistry and Histology of Glands of Cotton 43 1 



Furthermore, its pronounced toxicity may perhaps be regarded as a pro- 

 tective adaptation of the seed against animal attack. Haberlandt (4) 

 states that — 



excretory substances (in reservoirs of this type) are frequently made use of for 

 protection against animal foes. 



Withers and Carruth (ig) found rabbits much averse to cottonseed 

 kernels as a food, especially after once having been made sick. The 

 present writers have found no suggestion of such toxicity in quercetin 

 or its glucosids, but have had no opportunity to test them biologically. 

 Cook (j) credits the gland secretion with a repellent effect on the boll 

 worm, and discusses its possible value in repelling the boll weevil. He 

 finds that the relatively immune Kekchi cotton is usually punctured 

 only in areas free from glands, but states also that glands are especially 

 well developed in Mit Afifi and Egyptian cotton varieties particularly 

 favored by the weevil. Boll weevils which have been watched while 

 puncturing young plants seem to avoid the glands. 



Preliminary experiments were made to test the attraction for the 

 weevil of substances derived from the cotton plant. Of these the glu- 

 cosids quercimeritrin, isoquerceretin, and especially the steam distillate 

 and a volatile oil extracted therefrom appeared somewhat attractive. 

 These substances are largely localized in the interior glands. It is 

 possible, in view of the fact that the boll weevil has not been seen to 

 ptmcture the glands, that this attraction may consist in an odor which 

 suggests the presence of the cotton plant rather than in any actual food 

 value of the substances. The flavone substances possess no odor per- 

 ceptible to human senses; the volatile oil, on the contrary, has a pro- 

 nounced and characteristic odor. 



That the secretion of the glands is not repellent to all insects is shown 

 by the habit of certain aphids (Aphis gassy pii Glov.) in frequently 

 puncturing the glands of the mature leaves and in withdrawing part of 

 their substance (PI. 49, A). The flavones present seem not to be appre- 

 ciably diminished, and it is probable that the substance withdrawn by 

 the aphids consists largely of sugar (dextrose), traces of which can be 

 microchemically shown. This sugar may very likely be formed by the 

 hydrolysis of glucosids. The indifference of the boll weevil to sweet 

 substances has been previously noted by Hunter and Hinds (6). 



UNlVERSAIy PRESENCE Ot" INTERNAL GLANDS WITHIN THE GENUS GOS- 



SYPIUM 



Watt {18) makes the following statement : 



They [the glands] are, moreover, nearly universally present, though in some species 

 they are often obscured by the tomentum . 



He also refers to them in those of his specific descriptions which enter 

 into such comparatively minor details. A considerable number of species 

 of Gossypium in the National and Economic Herbariums have been exam- 



