The New Student's Reference Work/Chemotropism
Chemot′ropism (kē̇-mŏt′rō̇-pĭz’m), the sensitiveness of a plant to a onesided chemical stimulus (see Irritability) to which it responds by changing the rate of its growth in certain regions, and thereby putting the part affected in a new position with respect to the diffusing particles. It differs from chemotaxis only in the nature of the reaction. Diffusing gases or solutes (but usually the latter) may effect the reaction. Thus the growth of the germ-tubes arising from growing spores of fungi is directed by their chemotropism. When, for example, a spore falls upon a leaf on or in which the fungus can develop, it sprouts, and when the young germ-tubes reach the stomata (which see), they turn in and ramify in the interior. Or they may penetrate an epidermal cell at once. It has been shown in both cases that the directive influence is the presence of foods in the leaf. The pollen-tubes are similarly controlled in their growth down the style to the ovules (see Fertilization).