GUM, TANNIN, AND RESIN IN RELATION TO SPECIFICITY, ENVIRONMENT, AND FUNCTION

Abstract

The object of this paper is to show the taxonomic and climatic distribution of plants containing relatively large amounts of gum, tannin, and resin, and to determine the bearing of such facts on the functional importance of these substances. The chemical composition of gum, tannin, and resin leads one to consider a possible mutual association between them in the plant, for gums may be compounds of sugars, as is the case of pentosans; tannins may have sugar combined in their molecules, as is the case of tannin glucosides; and resins may contain tannin as well as gum in their aggregates, as is probably the case of gambir, gamboge, galbanum, and kino. It was thought worth while to investigate the occurrence of gum, tannin, and resin in plant families, genera, and species to determine a possible taxonomic relation between these constituents. A study of the distribution of these substances in plants is also of nterest in connection with their possible function. Gum is said to serve as a reserve food or to check excessive transpiration; tannin to protect against frost, animals, and fungi; and resin as protection in case of injury, and against animals and excessive transpiration. Protection against excessive transpiration is evidently most advantageous in desert plants and in evergreen plants in cold climates, so that agents useful in checking transpiration should be more common in these plants. Gum and resin should therefore be more abundant in plants subjected to excessive transpiration. Likewise a substance functioning as a protection against frost, as tannin is supposed to do, should be more abundant in temperate than in tropical regions. For these ecological reasons, therefore, a consideration of the distribution of plants containing gum, tannin, and resin is of interest. It is quite probable that most, if not nearly all, plants contain small amounts of gum, tannin, resin, and oil, and it is well known that a smaller number contain comparatively large amounts of these substances. It is widely known that some plants may have large amounts of one of these [The Journal for February (I7: I17-i85) was issued March I, 1930.] I87 13