Studies in the Energy Relations of Plants, 
I. The Increase in Area of Leaves and Leaf Surface 
of Cucumis sativus. 
BY 
9 
F. G. GREGORY, M.Sc. 
(. Department of Plant Physiology and Pathology, Imperial College of Science and 
Technology, London .) 
With fifteen Figures in the Text. 
A. Introduction. ■ 
I N view of the important role which the leaf surface plays in the economy 
of the plant it is surprising that no quantitative studies have yet 
appeared dealing with the increase in area of leaves of a plant measured 
from day to day. The difficulty which confronts the experimenter is to 
devise a method for obtaining the area of leaves without detaching them 
from the plant or injuring them in any way. The method here described 
was gradually elaborated in the course of a research on the physiology 
of forced plants carried out at the suggestion of Prof. V. H. Blackman 
at the Experimental and Research Station, Cheshunt, Herts., where the 
data for plants grown in sunlight were collected. The plant investigated 
was a variety of cucumber {Cucumis sativus, var. Butcher’s Disease 
Resister). 
B. Method of estimating Leaf Areas. 
The shape of the leaf is regarded as an approximation to a definite 
geometrical figure, of which the dimensions can be obtained 
and so the area calculated by the use of a suitable formula, 
Cotyledons. These approximate closely to ellipses, and 
the lengths of the major and minor axes (Fig. i, 2 a, 2 b) 
are obtained directly by applying a ‘ straight-edge ’ marked 
in centimetres and millimetres. The major* axis was taken 
as the length of the cotyledon from apex to base. The 
junction of the median and lateral veins was selected as 
the point at the basal end of the cotyledqn from which to 
measure. The minor axis was taken as the greatest width 
of the cotyledon. It has been the rule in this work to 
measure only to the nearest millimetre, as the errors of the method, which 
are discussed below, do not require any closer approach to accuracy. The 
[Annals of Botany, Vol. XXXV. No. CXXXV1I. January, igai.] 
Fig. i. 
