ABSOLUTE KATE OF GROWTH 



15 



the reliability and perfection of the apparatus. It also 

 shows that by keeping the external conditions constant, the 

 normal growth-rate can be maintained uniform for at least 

 15 minutes. As the growth when magnified 10,000 times 

 is nearly i cm. per second, and as it is quite easy to measure 

 0-5 mm., the Crescograph permits the record of a growth- 

 elongation of 0-00005 mm., that is to say, the sixteenth part 

 of a wave of red light. The absolute rate of growth, more- 

 over, can be determined for a period as short as 0-05 second. 



Fig. 5. Effect of temperature. 



Record on moving plate, where diminished slope of curve in the 

 second part denotes retarded rate under cold (Kysoor). 



These facts will give some idea of the great possibilities 

 of the Crescograph for investigations on growth. 



As the period of the experiment is very greatly shortened 

 by the method of high magnification, I have, in the deter- 

 mination of the absolute rate of growth, adopted a second as 

 the unit of time and [i or micron as the unit of length — the 

 micron being o-oooooi metre, or o-ooi mm. 



If in be the magnifying power of the compound lever, 

 and / the average distance between successive dots in milli- 

 metres at intervals of / seconds, then : 



I 



Rate of growth = — X 10^ [i per sec 



7nt 



