SOIL CONDITIONS AFFECTING PLANT GROWTH 35 



ence between sustained growth and the individual processes of 

 assimilation, etc. In the classical experiments of F. F. Black- 

 man and of Miss Matthaei (now A. G. L. Howard) (193) the 

 effect of temperature on assimilation, all other factors being 

 eliminated, was precisely that obtaining in an ordinary chemi- 

 cal reaction ; so also for respiration. Miss Matthaei found that 

 the amounts of carbon dioxide assimilated by a cherry laurel 

 leaf per 30 sq. cms. (about 8 sq. ins.) per hour at various 

 temperatures were : — 



Temperature, deg. C. 



Weight of CO2 as- 

 similated, grams . 



By interpolation, the values at 0°, 10°, 20°, etc., can be found, 

 and the rate of assimilation is thus seen approximately to 

 double for every increase of 10°, the usual order of increase in 

 chemical reactions : — ^ 



Temperature 



Amount of COg assimilated per hour 

 Increased rate for 10° C. 



But on the other hand, the effect of temperature on the rate 

 of growth of a plant as a whole is in no wise like its effect in 

 accelerating chemical change. Bialoblocki's (37) results with 

 barley were as follows : — 



The two curves are shown in Fig. 3 ; the difference between 



^The rates were maintained only for a short time at the higher tempera- 



tures. 



* A list of the papers dealing with the temperature co-efficient for cell growth 

 is given in Science, 6th November, 1908. See also Zaleski, W,, Ber. Deut. Bot. 

 Ges., 1909, 27, 56-62. 



3* 



