Morphology of reproduction in guayule and certain other species of Parthenium

Abstract

STUDIES on hybridization in guayule (Parthenium argentatum Gray) con- ducted under the Guayule Research Project of the United States Department of Agriculture at Salinas, California, revealed that apomixis occurred in this species (Powers and Rollins, 1945).3 This observation contradicts the reports in earlier morphologic work on guayule, according to which this plant shows no asexual reproduction (Kirkwood, 1910; Kokieva, 1932; Dianowa et al., 1935). A reinvestigation of the morphology of reproduction in guayule was therefore necessary. The present study on megasporogenesis, megagameto- genesis, and embryo formation of Parihenium was undertaken in response to this need. The first findings of these morphologic studies, which confirmed the conclusion of Powers and Rollins (1945) on the occurrence of apomixis in guayule, were reported in a preliminary paper (Esau, 1944b). Since then additional types ofguayule and two other species of Parthenium (P. hystero- phorus L. and P. incanum H.B.K.) have been examined, and the complete data assembled for the present paper.