30 WEEVIL-RESISTING ADAPTATIONS OF COTTON. 



NECTARIES Of THE LEAVES. 



The midrib of each leaf bears on the under side an oblong* pit, 

 from which a drop of nectar may often be seen to exude. This is 

 collected and eaten by the keleps, which are thus induced to visit 

 all parts of the plants, especially while they are still small. 



The habit of collecting the nectar was not previously known to 

 exist among the insects of the family (Poneridae) to which the kelep 

 has been referred. Nevertheless, the fact is not open to question. 

 The process is easy of observation in even greater detail than with 

 the true ants or the bees, because the keleps do not, like these insects, 

 have the art of regurgitating their food. They merely lap the nectar 

 up to form a drop, which, protected by the widely opened mandibles, 

 is carried into the nest to feed the queen and the young. 



Nectaries, or at least nectary-like depressions, are to be found 

 probably on the leaves of all varieties of cotton, though very small 

 and apparently inactive on some of the larger tree sorts. The 

 shape of the nectaries also varies greatly in the different species and 

 varieties, some being longitudinal, others transverse, and still others 

 crescentic or even sagittate. Some varieties have nectaries on the 

 three principal veins, and some even on five veins. 



The leaf nectaries of the Kekchi cotton are to be found on the 

 midrib of the leaf about 1.5 cm. from the base. They consist of a 

 rather shallow longitudinally oval depression surrounded by a broad 

 raised rim. The midrib often appears distinctly narrower above the 

 depression than below it, as though there were extra tissues to supply 

 it. The secretion is quite active, nearly all the nectaries showing a 

 small amount of liquid, which sometimes spreads out on the adjacent 

 surfaces. 



These nectaries furnish, as might be expected, a medium favorable 

 for the growth of molds or fungi, and there is often a considerable 

 network of dark-colored fungus mycelium creeping in and about the 

 moistened depressions, and with occasional erect, needlelike points, 

 which may be fruiting bodies. 



a This was not true, however, of a Mexican " tree cotton " of the Upland 

 type grown in the Department's experimental plots in Texas last year. Large 

 nectaries were generally present on three veins of each leaf, and the midvein 

 often had two. They were of the crescentic or sagittate type, but often 

 extremely long and distorted. Another Mexican tree cotton, with a different 

 type of lighter green foliage, suggesting that of Bixa, had nectaries only 

 on the midvein and these reduced to a narrow groove. The vein was not 

 thickened nor the margins raised. The two varieties were about as different 

 as could well be with respect to nectaries. Neither produced either flowers 

 or fruit, so that their true relationships were not to be ascertained. 



