52 PllESIDEXXIAL ADDRKSS SECTION C. 



CARBON ASSIMILATION. 



BY 



D. Thoday, M.A., F.R.S.S.Af., 



Profcasor of Boiany, University of Cape Town. 



Prcsideniial Address to Section C, delivered July 12, 1922. 



In expressing my appreciation of tlie honour of being 

 selected as President of Section C for this meeting I ask your 

 indulgence if I refer to a circumstance that makes the occasion 

 one of more than merely personal gratification to me. For the 

 first time in the history of the Association, the occupant of this 

 chair represents as his chief scientific interest the physiological 

 side of botany. 



It is only natural that in a young country with a flora so 

 rich and fascinating, South African botanists have paid more 

 attention to the systematic study and collection of that flora, 

 its geographical distribution and general ecology, and to the 

 morphology of the specially interesting and unique plants with 

 which it abounds, than to the more general or abstruse problems 

 of plant life. 



Work in these directions is useful and necessary. There still 

 remains mxich essential spade work to be done even in the col- 

 lection and determination of plants. There are signs, however, 

 that South African botany is developing beyond this essential 

 preliminary phase and that the time has arrived when more 

 attention will be paid, along with other fundamental branches 

 of the subject, to plant physiology. I do not think I shall be 

 accused of partisanship if I urge the paramount claims of this 

 field. 



The study of plant physiology, requiring, as it frequently 

 does, elaborate and expensive apparatus, presents special diffi- 

 culties in a country at an early stage of industrial development 

 and so far from the skilled instrument makei's to whom 

 European and American scientists have ready access. But for 

 a community which is largely agricultural this branch of botany 

 is of fundamental importance. The nutrition and growth of 

 plants form a very large part of its subject matter and these are 

 the daily practical concern of the farmer. It is therefore greatly 

 to be deplored that the staffs of the Agriculkaral Colleges and 

 Experiment Stations of the Union do not include one plant 

 physiologist. 



It is to some extent true that plant physiology' is applied 

 chemistry and physics, but this is by no means wholly true — not 

 yet. at any rate. Even were it so, chemists and physicists as 

 such lack an essential part of the equipment which is necessary 

 for the sohition, or even the clear realisation and analysis, of 



