AGRICULTURAL TEXT-BOOK. 43 



a fact which is practically important in the growth and quality of cer 

 tain grains. 



Upon every parallel of latitude, at all elevations above the 

 level of the sea, the same plant receives in the course of its ex- 

 istance an equal quantity of heat. 



132. The temperature of the soil, in summer, greatly exceeds 

 that of the air. At Albany, N. Y., the temperature of the soil 

 rises to 100 F. five feet below the surface, and to 140 half 

 an inch below. (Johnston.) But this temperature varies accord 

 ing to the color and quality of the soil, the evaporation, the 

 amount of water it contains, the nature of the subsoil, &c. This 

 internal heat is of great importance in practical farming ; a warm, 

 dry soil allowing the seeds to sprout early in the spring; forcing 

 forward the plant, as in a hot-bed; regulating the amount of 

 dew deposited; controlling early and late night frosts; and 

 probably influencing, favorably for the farmer, the growth of 

 parasitic fungi, such as rust, mildew, &c. It also causes manures 

 to act, and produces other beneficial effects, such as electrical 

 currents. It can be regulated and increased by artificial means, 

 but chiefly by proper drainage. 



133. Seeds require a given temperature of air and soil for 

 healthful germination ; various plants differing in this respect : 

 some requiring a much higher temperature than others. On 

 this point^ the following laws have been laid down : (a.) When 

 the temperature at noon is given, (other things being equal,) the 

 time necessary for the development of a seed may be ascer 

 tained, (b,) If the period of germination be given, the meridian 

 temperature of the country during the period may be deter 

 mined, (c,) &quot;When the seed fructifies in the same year in which 

 it is planted, the proper time for putting it into the ground is 

 when the meridian temperature is such as to produce vegetation 

 in the shortest period, (d,) An increase of temperature beyond 

 a certain point, does not expedite the vegetative process. 



The following table has been drawn up from actual experiment, 



