ii2 GROWTH 



although still proportional to the extant leaf area, is not 

 maintained but falls away in time. When grown under 



artificial light, 

 B * * * * results compar- 



52 ? ' able to those 



50 - grown in day- 



48[- %ht during December 



obtain. The detrimental 



, * factor is hard to formu- 



late: in December the 



14- 





904. 



' ^ 



42 

 40 

 38 

 36 

 34 

 32 

 30 

 28 



26 



24 . conditions which indicate that res- 



piration was intensified whilst carbon 



* low light intensity and the low 



temperature militate against 

 photosynthetic activity and 

 thus the amount of available 

 food may be adversely affected. 

 When grown under artificial 

 light, the energy value of the illumi- 

 nant was about equal to winter sun- 

 shine, but the temperature of the 

 greenhouse was that of the summer, 



assimilation was depressed. 



In this consideration mention has 

 been made of the law of compound 



22 

 20 



18 



15 1- interest and of the law of autocata- 



lytic reactions. 



V. H. Blackman * has drawn 

 attention to the fact that in many 

 natural phenomena the rate of change 



of some quantity is proportional to 

 the quantity itself. This is the law 

 of compound interest ; money left to 



3l_ accumulate at 



57911 13 15 17 19 21 23 25 compound in- 

 Atfe in days terest increases 



to an amount 



FIG. 9. Growth of the fruit of Cucurbita pepo ; . . . ob- ^ e ma gnitude 

 served value, x x x calculated value. 



* Blackman : " Ann. Bot.," 1919, 33, 353 ; " New Phytol.," 1920, 19, 97. See 

 also Kidd, West and Briggs : Id,, 88. 



