PROF. D. T. MACDOUGAL ON THE GROWTH OF 
Relation of the Growth of Foliage-Leaves A the Chlorophyll 
Function. By Danie, TazusLx MacBovaar, M.A., M.S., 
Assistant Professor of Botany, in charge of Plant Physiology, 
in the State University of Minnesota, U.S.A. (Communi- 
cated by Percy Groom, M.A., F.L.S.) 
[Read 18th June, 1896.] 
(Prate XIX.) 
Historical and General.—Investigation of the relation of the 
growth of leaves and their food-forming activity began with the 
work of De Saussure in 1804 (8), and since that time various 
phases of the subject have received an almost constant attention. 
However, it will be unnecessary to recount here the titles of the 
accumulated mass of literature, since all of the more important 
papers have been cited by Jost in a recent work to which 
frequent reference will be made (5). Broadly stated, the main 
purpose of the investigations described below may be said to be 
the determination of the extent to which leaves are dependent 
upon food-supplies constructed within their own tissues, and to 
what extent development may proceed at the expense of food 
stored in neighbouring or organically connected members, and 
also to ascertain if these relations may be modified. Ineidentally, 
attention has been paid to the causes operative in producing 
deterioration in certain leaves when grown under such conditions 
that food-formation could not be carried on. 
The result of such an enquiry, while of chief importance in the 
consideration of the characteristic physiological processes of the 
leaf, should be of valuein the interpretation of certain correlation 
phenomena, and also be of assistance in the delimitation of the 
principles governing leaf-expansion. 
A clear comprehension of the status of the subject may be 
gained by a brief consideration of the recent papers of Vines (9), 
Vóchting (10), and Jost (4 & 5)  Vines's investigations were 
concerned with the relation of growth to assimilation ; and from a 
series of experiments with plants in blue light, in an air free from 
CO,, in darkness, and without iron, he concludes that it is possible 
for leaves to grow when not assimilating, and that the retarding 
effect of light is exhibited by leaves not assimilating. Since the 
results of the growth of plants in an atmosphere fiee from CO, 
in the hands of different workers are so much at variance, it is 
important to note that in such experiments Vines used seedlings 
