Publication Date


Degree Program

Department of Biology

Degree Type

Master of Science


The major objective of the work was to clarify some of the adaptive mechanisms that a common widespread species would show as a possible requirement for survival in its natural habitats. Analysis of various populations of Xanthium (cocklebur) indicated differences in chlorophyll levels and leaf chloroplasts ultrastructure between populations. The study also revealed some insight into intrapopulational variation in dark requirements for flowering of selected populations. In addition, caloric values of dried leaf material of cocklebur were analyzed for interpopulational differences. It was evident that higher chlorophyll levels are correlated with increase in latitude of origin and a corresponding decrease in growing season. The limited examination of leaf ultrastructure indicated the manner in which the higher chlorophyll levels are contained. Caloric values of leaf material showed lower total productivity in Texas populations. Variations found in the flowering response of the Tennessee population also gave evidence of the need for further study of plants from that area in relation to correlating that particular population with the other populations in the study.


Medical Sciences