170 



GROWTH 



is equivalent to 16-5 per cent, of the dry weight of the plant. 

 A similar relation is shown by Oxalis, a shade plant, but the 

 amounts are much smaller ; 0-8 mg. of carbon dioxide being 

 assimilated per 50 sq. cm. per hour at 20° C, whilst the loss 

 due to respiration is 0-15 mg. at the same temperature for the 

 same units. 



The following table gives Boysen-Jensen's results for 

 various plants. The figures for respiration are milligrams of 

 carbon dioxide given out per 50 sq. cm. of leaf surface per 

 hour at 20° C, and those for assimilation are milligrams of 

 carbon dioxide synthesized by the same area, in the same 

 time and at the same temperature. All the figures are 

 maximal values : — 



In all these plants the carbon assimilation is much greater 

 than respiration, and since the amount of synthesized material 

 is more than enough to provide for respiration during the 

 hours of darkness, growth takes place. This is illustrated in 

 the following table which represents the percentage of in- 

 crease in the dry matter of Sinapis alba. 



The flowering period occurred early in June which resulted 

 in a fall (Fig. 7). When these figures are plotted, an Sshaped 

 curve is formed which, as will be seen later, is typical of 

 growth curves. 



In further illustration a saprophyte may be taken : Ter- 



