no GROWTH 



The fact that the curve for leaf area per unit dry weight 

 corresponds with the growth rate curve indicates the close 

 physiological connexion between the relative growth rate and 

 carbon assimilating area per unit of dry weight (Fig. 7). The 

 correspondence, however, is not precise ; instead of showing 

 a definite type of variation, as does the relative growth rate, 

 the leaf area per unit dry weight curve fluctuates about a mean 

 value. These fluctuations are due to the conditioning factors 

 of growth of which factors temperature is amongst the most 

 significant. The importance of leaf area in the economy of the 

 higher plant is so obvious that no elaboration of the statement 

 is required. The growth in area of the leaves of the cucumber 

 has been closely studied by Gregory* and may be alluded to at 

 this stage in that it introduces some aspects of growth which 

 properly belong to a general consideration. But before this is 

 done, the " grand period of growth " must be recalled to memory. 

 As is well known, Sachs used this expression to designate the 

 period through which the plant, or plant member, exhibits its 

 sequence of growth rates. Thus the growth rate of the first 

 internode of Phaseolus multiflorus is at first slow, then quickens 

 to a maximum, after which a decrease in the rate to zero obtains, 

 which point is coincident with the attainment of maturity. 

 The sequence is illustrated in Fig. 8 which is based on Sachs's 

 measurements. 



The grand period of growth does not include an analysis 

 of the fluctuations in the rate during the periods between the 

 measurements; thus the growth rate between the third and 

 fourth day is the summation of the growth during that period. 

 Priestley and Evershed f in their study on the root growth of 

 Tradescantia and tomato, based on the increase in dry and wet 

 weights of the roots produced on cuttings, find the curves ob- 

 tained are a sequence of these grand period curves which are 

 a series of S curves, a type which is very common in graphs 

 illustrating growth phenomena (see Fig. 9). The time of 

 transition from one S curve to the next coincides with the time 

 of appearance of a crop of roots of a subordinate branch order. 



Gregory found that the growth in length, in breadth, and 

 in area of the leaves of Cucumis sativus show a grand period 



* Gregory: "Ann. Bot.," 1921, 35, 93. 



t Priestley and Evershed : Id., 1922, 36, 225. 



