Contents

03 January 1986
Vol 231, Issue 4733

About The Cover

Two spheroids (individuals) of the green alga Volvox carteri. The lower spheroid is asexual, with sixteen large reproductive cells that divide to produce a new generation, which is normally asexual also. But when heat shocked, females produce egg-bearing sexual daughters (shown above) and males produce sperm-laden sexual sons. Then eggs and sperm combine to produce heat- and desiccation-resistant zygotes. See page 51. [David L. Kirk, Washington University, St. Louis, MO 63130]