176 



GROWTH 



increase, although still proportional to the extant leaf area, 



not 



54 



52 

 50 

 48 

 46 

 44 

 42 

 40 

 38 

 36 

 34 

 32 

 30 



28 



26- 

 24- 

 22 

 20 



18- 

 16- 

 14- 



fflO 



c 



8 

 6 



*9°4 - 



2 b 





is not main- 



« * * * tained but falls 



* • 



* • away in time. 



When grown 

 ' under artificial light, re- 



suits comparable to those 

 grown in daylight during 

 December obtain. The 

 detrimental factor is hard to 

 formulate : in December the low 

 light intensity and the low tem- 

 perature militate against photo- 

 synthetic activity and thus the 

 amount of available food may be ad- 

 versely affected. When grown under 

 artificial light, the energy value of the 

 illuminant was about equal to winter 

 sunshine, but the temperature of the 

 greenhouse was that of the summer, 

 conditions which indicate that respira- 

 tion was intensified whilst carbon as- 

 similation was depressed. 



In this consideration mention has 

 been made of the law of compound 

 interest and of the law of autocatalytic 

 reactions. 



V. H. Blackman * has drawn at- 

 tention to the fact that in many natural 



phenomena the 



rate of change 



of some quan- 

 tity is propor- 



. . observed value, 



5 7 9 11 13 15 17 19 21 23 25 

 Af3e in days 



Fig. 10. — Growth of the fruit of Cucurbita pepo ; 



xxx calculated value. 



* Blackman : " Ann. Bot.," iqiq, 33» 353 I " New Phytol.," 1920, 

 19, 97. See also Kidd, West and Briggs : id., 88 ; Schmidt : " New Jersey 

 Agnc. Exp. Sta.," Bull. 404, 1924. 



