276 THE SMALL GRAINS 



290. Heat requirements in cereal development. 

 The variation in length of the fruiting period indicates 

 that the total heat required for maturing the kernel is 

 furnished quicker in one place or in one season than in 

 another. In Europe, considerable study has been given 

 this subject for more than 150 years, particularly in an 

 effort to secure some thermometric constant by which 

 may be calculated the total heat required for maturing 

 a given crop in a given locality. Gasparin, Marie-Davy, 

 Linsser, Angot, and others have investigated the subject. 

 In calculating the sum total of heat, one thing was cer- 

 tain, that all temperatures included should be above a 

 certain minimum necessary for plant growth. This 

 minimum was variously stated to be from C. to 6 C. 

 The sum of all mean daily temperatures above a minimum 

 of 6 C., for instance, during the life of a crop, would 

 constitute the sum total of heat required for maturity of 

 that crop. 



291. Linsser 's Law. Is the sum total of heat required 

 the same for the same crop in every locality? Linsser 

 decided not, and made the following statement known as 

 " Linsser 's Law " : In two different localities the sums 

 of positive daily temperatures for the same phase of vege- 

 tation are proportional to the annual sums total of all 

 positive temperatures for the respective localities. A 

 natural corollary from this law is that seeds taken from 

 high latitudes or altitudes to lower ones, tending still to 

 utilize the same proportion of the total annual heat which 

 was less in the former localities, will ripen earlier than the 

 native crops of the warmer localities. This corollary, if 

 true, may explain a fact well known to agriculturists, 

 that spring varieties brought from the north usually ripen 

 earlier than native varieties. The fractional part of the 



