122 
Gregory. — The Increase in Area of Leaves and 
autocatalytic reaction in which the material catalysed gradually decreases 
in amount as the reaction proceeds. A modification of this formula is intro- 
duced to represent the growth in area of single leaves under artificial light. 
The increase in area of the total leaf surface of plants grown in day- 
light in March and June closely follows a compound interest law, the rate 
of increase at any time being proportional to the area existing at that time. 
For plants grown in December, however, the increase in total leaf area 
follows a more complex law, which may be represented by the function 
A — ae r log 1 = af ; the rate of increase at any time is then given by the 
equation showing that the rate of increase is still proportional to 
the leaf area already extant, but tends to fall off with time, owing to the 
action of a detrimental factor. In the case of plants grown under artificial 
light, the increase in total leaf area is found to follow the same law as for 
plants grown in full daylight in December, and also shows the action of 
a detrimental time factor. It is suggested that the detrimental factor in 
this case may have been due to the high temperature maintained during the 
experiment. 
It is shown that under comparable conditions the ‘ average leaf area ’ 
is determined by the product of intensity and duration of light radiation. 
In support of the compound interest law of leaf-surface growth coeffi- 
cients are quoted for correlations between 
(i) maximum area of cotyledons and maximum area of ist leaf: 
r = + o-54 ; 
(2) maximum area of cotyledons and dry weight of plant after 30 days : 
r — + 0-36 ; 
(3) growth-rate and crop weight : 
r = + 0*7. 
In conclusion, the author wishes to record his thanks to Prof. V. H. 
Blackman for his unfailing inspiration and continual interest in the progress 
of the work ; to Mr. A. B. Lister, secretary to the Experimental Station, 
Cheshunt, for many facilities for the work ; and to Miss H. Marchant, 
laboratory assistant of the Experimental Station, for assistance in collecting 
data under very trying conditions. 
Bibliography. 
Blackman, V. H. : The Compound Interest Law and Plant Growth. Ann. of Bot., vol. xxxiii, 
P- 353- I 9 I 9* 
Enriques. P. : Wachstum und seine analytische Darstellung. Biol. Centralblatt, Bd. xxix, 1909. 
Gericke, F. : Experimented Beitrage zur Wachstumsgeschichte von Helianthus annuus. Zeit. f. 
Naturwiss., Bd. lxxx, p. 321, 1908* 
