Dew and the growth of the uredospore germ tube of Puccinia graminis on the wheat leaf

Water droplets simulating dew, formed on wheat leaves held in a condensation chamber, appeared first on the leaf hairs and coalesced into lines along the ridges of the leaf surface in close proximity to the stomata. On leaves thus wetted, germ tubes from uredospores of Puccinia graminis showed a thigmotropic response, growing at right angles to the ridges: when they reached the stomatal region the penetration of the stoma may be further assisted by chemotropic or hydrotropic attraction. Studies on plastic surfaces showed that germ-tube growth took place only between and not within water droplets.