Distribution of the Bitter Principle in the Shoot of Helenium tenuifolium

Abstract

1. Microchemical tests on freehand sections from the leaves, stems, and flowers of Helenium tenuifolium Nutt. show the bitter principle, a mixture of tenulin and isotenulin, to be present in traces in all tissues and in a concentrated form only in two types of trichomes which appear in groups of three in surface depressions on mature plant parts. 2. Each group of three trichomes originates from three adjacent epidermal cells on the unindented surface of the organ primordium. In the mature leaf the depressions result from a retardation of palisade development adjacent to the epidermal cells bearing the trichomes. 3. Tenulin and isotenulin accumulate within the two slender lateral trichomes of each group and within and upon the outer wall surfaces of the large central trichome. The latter is formed by stratified cells loosely surrounded by a cuticle which becomes distended from the accumulation of water and tenulins in the subcuticular space.