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Cotton plants have both external and internal glands. The external glands are called "nectaries" and secrete a sweet fluid. There are four sets of nectaries, one inside the flower and three extrafloral. The number and development of extrafloral nectaries vary considerably in different species. The secretory part of the nectary includes numerous glandular hairs, or papillae. A second set of nectaries is found outside of the calyx near its base. As a rule, this set consists of three irregular triangular shaped nectaries. A third set, consisting of three nectaries is located on the pedicel of the flower, one being near the point of attachment of each bractlet. Also on the underside of foliage leaves, a nectary is located on the midpart of the largest vein. Frequently two others are located in similar places on two other large veins of the leaf.
Internal glands are found heavily distributed over the entire plant, except for the root. They appear as small dark black specks, known as "black glands, oil glands or resin glands." They also appear in cotyledonous part of the seed. These glands when exposed to light contain anthocyanin in border cells, and the secretion contains resin, ethereal oil, quercetin and tannins. Glands not exposed to light do not show any anthocyanin and contain a toxic compound called "gossypol." (Brown, p.107)
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