202 Leaf-Product [400 
LEAF-PRODUCT AS AN INDEX OF GROWTH IN 
SOY-BEAN 
By F. Merritt HILDEBRANDT 
It has been pointed out by McLean* that the sum of the 
products of the length and breadth of all the leaflets on a 
soy-bean plant 4 weeks old is approximately proportional to 
the total leaf area of that plant, and he adds that the leat 
area is itself nearly proportional to the total dry weight of 
stem and leaves. The sum just mentioned has been called 
the leaf-product by the same writer, his observations being 
based on measurements obtained at two stations in Maryland, 
Easton and Oakland, in the project carried out during the 
summer of 1914 by the Maryland State Weather Service in 
co-operation with the Laboratory of Plant Physiology of the 
Johns Hopkins University. That project included similar 
studies of the relation of plant growth to climatic conditions 
at seven other stations in Maryland, besides Easton and Oak- 
land, and the present paper aims to bring out the fact that 
this interesting relation between leaf-product, leaf area and 
dry yield of tops applies generally to the soy-bean data for 
all nine stations. 
If the method proposed by Livingston? and McLean, of 
employing the growth rates of standard plants as indices for 
the comparison of different climates as these influence plant 
growth in general, is to be of value, it is of course necessary 
that suitable plant characteristics be chosen for measurement 
in determining the growth rates, and it is desirable that the 
measurements be such as may be made from time to time 
without injury to the plants. The most generally accepted 
*McLean, F. T., “A preliminary study of climatic conditions in 
Maryland, as related to plant growth.” Physiol. Res. 2: 129-208. 
1917. 
* Livingston, B. E., and McLean, F. T., “A living climatological 
instrument.” Science, n. s. 43: 362-363. 1916. : 
