AVERAGE RATE OF GROWTH 1 3 



a detached organ, the exposed cut end being wrapped 

 in a moist cloth. The shock-effect of section disappears 

 in the course of a few hours, after which the isolated organ 

 renews its normal rate of growth. Of the different 

 specimens, the plant Scirpus Kysoor offers special advan- 

 tages ; its leaves are much stronger than those of Wheat 

 and other grasses, and can bear a certain amount of pull 

 without harm. Its rate of growth under favourable seasonal 

 conditions is considerable : some specimens were found 

 to have grown more than 8 cm. in the course of 24 hours, 

 or more than 3 mm. per hour. This was during the rainy 

 season in the month of August : but a month later the rate 

 of growth had fallen to less than i mm. per hour. 



I will now describe certain typical experiments which 

 will show (i) the extreme sensibihty of the Crescograph, 

 and (2) its wide applicabihty in different investigations. 

 The capabihty of the apparatus in the accurate determina- 

 tion of the time-relations of responsive changes in the rate 

 of growth will be described in a later chapter. 



In order to ensure regularity in the rate of growth, the 

 plant should be kept in uniform darkness or in uniformly 

 diffused light. So sensitive is the recorder that it shows 

 a change of growth-rate due to the slight increase of illumi- 

 nation caused by the opening of an additional window. 

 One-sided light should be avoided, as it gives rise to dis- 

 turbing phototropic curvature. Temperature and hygro- 

 metric condition must be kept constant. After observing 

 these precautions, the growth-rate of vigorous specimens is 

 found to be very uniform. 



The records are taken either on a stationary plate or 

 on a plate which moves past the writer at a uniform rate. 



Stationary Plate Method. — A record, which is vertical, 

 is first taken, to ascertain the normal rate of growth. 

 Then, in order to study the effect of some changed condition, 

 the recording plate is moved i cm. to the left ; the tip of 

 the writer is brought once more to the bottom by means of 

 the fine screw adjustment S (see fig. 3) and another record 



