1910.J 



Vitality of Farm Seeds. 



563 



valuable information as to the probability of frost. For frost 

 to be formed, the dew-point near the ground must be below 

 32 0 F., when the deposited water at once takes the form of ice.. 

 If the air be very dry, the temperature may fall low enough 

 to injure vegetation without the formation of frost, i.e., by 

 what is known as a black frost. If the air be very moist, 

 the condensation of vapour as dew may begin before the 

 temperature of 32 0 F. is readied, and the latent heat liberated 

 by the condensed water will frequently prevent the forma- 

 tion of frost. Hence the value of ascertaining whether the 

 clew-point is above or below 32 0 F. ; if above, as a general rule 

 frost need not be feared unless the wind is still bringing 

 colder air from neighbouring regions. The conditions 

 favourable to frost are : (1) clear skies, with little wind 

 movement; (2) a certain (but not excessive) amount of 

 moisture in the air; and (3) high atmospheric pressure. The 

 value of observing the dew-point was shown in the above 

 experiments, in which it was found that the dew-point re- 

 corded in the evening was not far at any time from the 

 lowest temperature recorded during the night following. A 

 useful instrument is a thermometer which can be set to ring 

 an electric bell at a given temperature. 



The length of time during which seeds, especially farm 

 seeds, retain their vitality or capacity to germinate is of 



considerable interest, for it is some- 

 Vitality of times important to know the maximum 



age at which seeds may be expected to 

 yield what may be regarded as a successful crop. A not 

 uncommon view is, that it is safe to sow cereal grains two 

 years old, while peas and beans, mangolds, cabbage, and 

 similar seeds may be sown up to four years old. This does 

 not mean that older seeds will not germinate at all, but that 

 they will in general be unlikely to yield good results in prac- 

 tical farming, Broadly speaking, it is inadvisable to sow 

 old seeds, and any monetary advantage which would be 

 gained thereby would rarely be sufficient to compensate for 

 the probable loss of germinating power. It is sound practice 

 to sow only healthy, clean, pure, strongly-germinating seeds 

 of the previous year's growth. 



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