The proposals put forward in this paper have arisen out of discussions between botanists and zoologists at meetings of the Taxonomic Principles Committee of the Systematics Association extending, with interruptions, over a period of nearly 16 years. (The Systematics Association was founded in 1937 under the title of 
The Association for the Study of Systematics in Relation to General Biology
. The present secretaries are MrR. D. Meikle, Royal Botanic Gardens, Kew, Surrey (Botany), and DrJ. Harding, British Museum (Natural History), Cromwell Road, London, S.W.7. (Zoology)). About two years ago some of the botanists connected with that Committee felt that further progress in discussions on the terminology of the units of micro-evolutionary change might be best attained if a group of botanists could reach agreement on certain definite proposals which could then be considered by their fellow botanists and by their zoological colleagues. Accordingly a number of meetings for this purpose were held during 1952 and 1953 and a considerable measure of agreement was reached.We are authorised to say that the following botanists who took part in the discussions are in general agreement to test the scheme now advanced: — DrJ. G. Baker (Botany Department, Leeds); Mr.B. L. Burtt (Royal Botanic Garden, Edinburgh); Dr.J. W. Gregor (Scottish Plant Breeding Station, Corstorphine, Edinburgh); Dr.Y. Heslop-Harrison (Dept. of Botany, University College, London); DrW. B. Turrill (Royal Botanic Gardens, Kew); ProfessorD. H. Valentine (Botany Department, Durham); DrS. M. Walters (The Botany School, Cambridge); DrE. F. Warburg (Botany Department Oxford).
We are grateful also for criticisms and suggestions received from other colleagues, in particular from Prof.J. B. S. Haldane.