142 



RELATIONS OF SOIL TO HEAT 



series the barley plants were allowed to develop for two 

 months at the temperature of the air before the temperatures 

 of the soils were altered ; in consequence of this change in 

 the method, the ill effect of the higher temperatures is less 

 apparent in this series than in the first. 



TABLE XXIV 



INFLUENCE OF SOIL TEMPERATURE ON THE YIELD OF BARLEY 



A soil temperature of 50 F. was apparently sufficient for 

 the normal development of the barley plant, but the ripening 

 of the crop was slow, and none of the corn was more than 

 milk-ripe when the experiment concluded. The soil tem- 

 perature of 68 gave a larger produce and better ripened ears. 

 With much higher soil temperatures the amount of produce 

 was much reduced. 



In an experiment lasting only twenty days, it appeared that 

 the optimum soil temperature for wheat was somewhat higher 

 than that for barley, and this again somewhat higher than 

 that required by rye. 



The great influence of soil temperature on plant growth is 

 well known to gardeners, who frequently employ hot-beds, 

 and make use of a bottom heat for striking cuttings and 



