The earliest embryonic stages, because of the simplicity of their organization and cellular structure, are logical starting points for developmental studies of plants as a whole. The zygote and early post-zygote phases of embryonic development are periods of minimum cell form differentiation, if the cells possess a potentially to develop in a number of different ways at any stages in their development, it is in all likelihood at this early date. Becoming more and more specialized with continued growth, they finally form tissues and organs with the capacity for specific functions in the division of labour of the mature plant organization. it was felt that the more specialized the cells became, the less impressionable they would be to the influence of an in-vitro environment. Accordingly, this treatise deals with the culture in artificial medium of the early post-fertilization periods in the embryonic growth of Pinus nigra, var. austriaca, in an effort to discover and assess those factors which influence and govern the embryonic development pattern. The present study was begun in 1951 at the suggestion of Professor N.W. Radforth. I wish to express my appreciation to Professor Radforth for his guidance in conducting my research, without which this investigation could not have been carried out. This work was undertaken as part of a programme which has been assisted through a grant from the Ontario Cancer Treatment and Research Foundation, for which Dr. Radforth is the grantee. / Thesis / Master of Science (MS)

Little is known about funda­mental mechanisms of growth control on the growth ff single or small groups of cells of the higher plants. Study of these effects in vitro requires the knowledge of the primary conditions for growth in vitro. In this work a procedure was outlined and used in an ef­fort to establish a basis for the standard procedure. Also the associated effects of the physical, and to some extent, the chemical environment on the growth of the proembryo and prothallium. of Linus were studied. / Thesis / Master of Science (MS)