Surface anatomy of weed leaves with particular reference to stomata

Thirty-five species of weeds were grown in a field nursery in order to obtain comparable data on the number, size, and surface distribution of their stomata. Mature leaves were cleared, stained, and mounted for microscopic examination. The mean numbers of stomata per mm² of leaf surface ranged from 2.3 to 294.9. The mean lengths varied from 21.6μ to 59.0μ . Twenty species had more stomata on the lower than on the upper surface, while only 3 species had significantly more on the upper than on the lower surface. Between species there was negative correlation of stomatal density with length, but between surfaces within species, the lengths remained fairly constant despite differences in stomatal densities. Plants grown in partial shade had relatively more stomata/mm² than those grown in full sun. Similarly, leaves taken in July had a greater density of stomata than those harvested in June. In neither case could the differences be attributed to environmental factors, alone. A slight but significant correlation of stomatal density on the upper surface with known susceptibility to 2,4-D was detected. A greenhouse experiment using picloram sprays on 3 of the species, indicated greater penetration associated with dense stomata on the lower surface than with sparse stomata on the upper surface. A series of drawings were done depicting the different stomatal characteristics and types of trichomes. It was estimated that the leaves of 9 species were sufficiently hairy to influence retention or penetration of sprays.Land and Food Systems, Faculty ofGraduat