§1] 



UPON THE RATE OF GROWTH 



461 



it is not constant for a given difference between tlie two tem- 

 peratures, but is greater in raising the temperature from 5° to 

 18° than in raising from 17° to 30°. The more abnormal one 

 of the pair of temperatures is, the greater is the response. 



c. Cause of Acceleration of Growth hy Heat. — The accel- 

 eration of growth may be clue either to increased assimilation, 

 imbibition, or production of formed substance. Is it princi- 

 pally due to any one of these or are all increased in the same 

 proportion ? Data on this subject are afforded by certain 

 measurements made by Bialoblocki ('71). 



Seeds of rye, barley, and wheat were planted in soil which was fertilized 

 by nutritive solutions and heated by a surrounding bath of water. The 

 average absolute weight of the whole plant of each species was determined 

 after the lapse of twenty days. The proportions of water, organic matter, 

 and ash in the entire plant were likewise determined. Some of the results 

 are given in Table LIV. It is to be noted that the high temperature was 

 applied only to the soil in which the roots of the plant were imbedded. 



TABLE LIV 



Giving the Average Weight (in Milligrammes) and the Percentage op 

 Water in Plants whose Roots are maintained in Soil, at Various- 



Temperatures, FOR 20 Days (Bialoblocki) 



-^ 



> 



This table shows that the percentage of water increases slightly 

 but constantly as the growth is accelerated by increased tem- 

 perature, reaching a maximum near the optimum temperature. 

 Other data (not reproduced here) show that the percentage of 

 ash remains about constant, while that of dry organic sub- 



