We have developed several strains of cotton, Gossypium hirsutum L., which are resistant to tobacco budworm, Heliothis virescens Fab. We also have available from the cotton collections several lines of Asiatic cotton, G. arboreum L. We examined the number of gossypol glands in plant parts from several upland and asiatic lines to determine if number of glands was related to resistance to tobacco budworms. Parrott, in our laboratory, observed that young larvae feed on the bracts of very small squares in terminal areas of plants. We thus counted glands on the entire surface of bracts of squares, 2 mm on a side collected from the terminal area of several cotton strains. By a sampling procedure all glands visible to the unaided eye were counted on one of the ribs running from the base of the bract to the tip of the teeth. We also counted glands in terminal leaves about 10 cm², in petals, the calyx and in the lobes of the calyx. Day old bolls were dissected laterally at their widest diameter, and glands were counted in the carpel wall on the circumference of the cut boll.

Glands In all the asiatics were less dense in leaf tissue, and they were more dense in bracts, petals, calyx and carpel walls of some asiatics than in 'Stoneville 213' (St 213). This distribution and density of glands in the asiatics may be partially responsible for asiatics, in general, being no more susceptible to tobacco budworms than St 213.

Gossypol gland density on the bract and calyx seems to be an important component of resistance to tobacco budworm. In the Asiatic cottons, we found a general distribution of glands on the bract and, generally, an abundance of glands in the calyx lobe. This is in a diploid species which has only the G12 locus. This contrasts with the distribution of glands in a typical upland cotton, such as St 213, which is generally void of glands In the calyx lobe and in the mid part of the bract. Each of these are sites of concentrated feeding by young budworm larvae.

We have a great diversity in size of glands in some of our experimental strains. The use of dense, small glands may be a useful approach to resistance. The placement of glands in the calyx lobe and general distribution in the bracts may be a second approach. W. P. Sappenfield suggested several years ago that the density of the glands in the calyx lobe of high gossypol breeding material could be used to select for plants high In square bud gossypol. Recent research by Lee has suggested the high gossypol breeding material from Lukefahr's XG-15 Soccorro Island source had a special allele (Gl(3)r), at the Gl(3) locus. We are, however, suggesting that it may be possible to increase the density of glands In the calyx lobe and to obtain a general distribution of glands in the bract without resorting to the special Gl(3) high gossypol allele. Evidence from our experiment with the asiatics suggest that it may be possible to do so. We plan to look for this character in upland cottons. We will be particularly interested in this approach if it does not increase the gossypol level in the seed.