BY PETER D. MOORE
Department of Biology
King’s College
London, U.K.
" Many plants respond to grazing by increasing their production of secondary chemical compounds that play a deterrent role. Stinging nettles (Urtica dioica) from heavily grazed habitats are found to possess higher densities of stinging hairs than those from ungrazed areas, and experimental damage to plants in the laboratory also results in higher trichome density on the new shoots.
A.S. Pullin, J.E. Gilbert, “The stinging nettle, Urtica dioica, increases trichome density after herbivore and mechanical damage,” Oikos, 54,275-80, March 1989. (Oxford Polytechnic, Headington, Oxford, U.K.)
" Mystery still surrounds the extinction of the North American megafauna around the end of the last (Wisconsin) glaciation. The contention that over 30 genera died out between 12,000 and 10,000 years ago now looks invalid—only about seven genera (including mammoth and Shasta ground sloth) are well dated to this period; precise time and ...
