RATE OF GROWTH 



175 



of growth when grown in natural conditions ; but, when 

 continuously illuminated by electric light, a method some- 

 times adopted by market gardeners to secure early crops, the 

 rate of increase falls from the first measurement of area. The 

 curves of increase in linear dimensions and in area can be 



14 



10 

 9 



7 

 6 



e5 



E 



c 



O 

 £ 1 



Temp. 1275° -13 75° C 



12 3 4 5 6 7 8 9 



Time in days 



Fig. 9. 



10 



represented by the formula of an autocatalytic reaction.* 

 The increase in area of the total leaf surface varies with the 

 season of the year : in March and June in daylight, the rate of 

 increase is proportional to the area existing at that time, that 

 is, the growth follows a compound interest law ; but during 

 December a detrimental factor intervenes so that the rate of 



* This term is explained on p. 178. 



