THE INVOLUCRE AS A PROTECTIVE STRUCTURE. 37 



the jDlant avus searched foi nectaries. It was noticed by Mr. Kinsler 

 that the keleps seemed to be giving especial attention to the midrib 

 near its junction with the veins of the lower divisions of the leaf. 

 Our lenses then revealed the fact that there are two minute raised 

 wings or margins running along the ui)per side of the midrib and 

 petiole, forming two narrow grooves in which the nectar is evidently 

 secreted. The grooves are also protected by a row of fine hairs which 

 project across Ihem from the raised margin. The behavior of the 

 kele^D thus receives a practical explanation, and the tshubai finds a 

 regular place next to the cotton among the plants protected by the 

 kelep. The nectar-secreting habit of the tshubai may also explain 

 its being eaten so readily by stock, and nui} helj) to give it standing 

 as a forage plant, in spite of its weedy and unpopular relatives. 



A second member of the eonqjosite family often visited by the 

 kelei^s is the '* sajal."" a species of Melanthera (probably M. (leltoidea). 

 Avhich also has hjcal value as a forage plant. I)eing eaten greedily 

 l)y horses and mules, even in preference to grass. No nectaries have 

 been found on this. A third composite, not yet identified, produces 

 nectar in small depressions at the base of the leaf on the under side. 



THE INVOLUCRE AS A PROTECTIVE STRUCTURE. 



0- 



Cotton is the only plant known to be attacked bv the boll weevil, 

 and it is also unique among its relatives in the possession of a large 

 leafy involucre. This nuiy be a mere coincidence, or it may be that 

 the weevil has had a considerable influence in the development of the 

 involucre, depending upon the antiquity of the contact between the 

 insect and its host plant. The involucre has. it is true, functions 

 other than the exclusion of the weevils, since it takes the place of the 

 calyx in protecting the young bud, but the reduction of the calyx 

 probably followed the enlargement of the bracts, instead of preceding 

 it. But however originated, the large bracts have, at the present 

 time, a definite value in the problem of weevil resistance. There are 

 several specialized characters which appeal- as though definitely cal- 

 culated to increase the efficiency of the involucre in excluding the 

 weevils from the young buds. 



INVOLUCRAn BRACTS (JROWX TOGETHER. 



Both the Kekchi and Rabinal cottons frequently have the involucre 

 closed at the base, the three bracts being grown together, thus making 

 it impossible for the Aveevils to enter from below. In the Sea Island 

 and Egyptian varieties, as well as in some of the Upland sorts, the 

 bracts are not merely divided to the base, but they often have the 

 lower corners rolled back, thus leaving an open passage for the 

 weevils. The Rabinal cotton much excels all the other varieties thus 



