[427] SCIENTIFIC MANUAL. 141 



light, is essential to vegetation, and is required in different 

 degrees for the normal development of different plants. 



The following table taken from/'How Crops Grow," shows 

 the results of experiments conducted by Sachs to ascertain 

 the extreme limits of warmth at which the seeds of some 

 of the principal agricultural plants will germinate : 



Lowest Highest T T P f 2 tur ?, of 



Temperature. Tempe.ature. ^1*^1 



Wheat 41 F 104F 84F 



Barley 41 104 84 



Pea 44.5 102 84 



Maize 48 115 93 



Scarlet-bean 49 111 79 



Squash 54 115 93 



The warmth of soils is influenced by various circum- 

 stances, such as texture, color, composition, exposure, 

 drainage, etc. 



The following table taken from " How Crops Feed," 

 shows the relative " capacity fouheat " of different soils. 

 That of lime sand being assumed as 100. Schubler heated 

 a given volume of soil to 145F, placed a thermometer in 

 it and observed the time required to cool down to 70, the 

 temperature of the atmosphere being 61F. In one 

 column are stated the times of cooling, in another the 

 " relative power of retaining heat, or capacity for heat. " 



Substance. Time of Cooling. Capacity for Heat. 



Lime Sand 3 hours. 30 Minutes. 100 



Quartz Sand. 



Clay Loam 2 



Clay Plo$v Land 2 



Heavy Clay 2 



Pure Gray Clay 2 



Garden Earth 2 



Humus.. ..1 



27 

 30 

 27 

 24 

 19 

 16 

 43 



95.6 

 71.8 

 70.1 

 68.4 

 66.7 

 64.8 

 49.0 



" It will be seen that the sandy soils cool most slowly, 

 then follows clays and heavy soils, and lastly comes 

 humus." 



The times of warming of the same soils would corres- 

 pond with that of cooling if containing but little moisture 

 and exposed to a low temperature. 



