24 PRINCIPLES OF GARDENING. [CH. I. 



growth in which it occurs. The shanking in grapes 

 appears traceable to this cause. 



Then again, a soil abounding in supei'fluous \Yater 

 is always colder than a soil of siinilai' constitution 

 that has been well drained. The reason for this is 

 obviously that the same quantity of caloric which will 

 heat the earth four degrees will only heat water one 

 degree ; or, to use the language of the chemist, tlie 

 capacity for heat of water is four times greater than 

 that of the earth s. In every day experience, we see 

 the low lying and consequently the wettest portions 

 of a field, are always those on which the even- 

 ing mist or fog first appears ; for at one season of 

 the year it becomes colder than the air, and the at- 

 mospheric moisture always precipitates first on the 

 coldest surface. At other seasons of the year, eva- 

 poration from the wettest portion of a field is tlie 

 most abundant ; and, at those seasons, mists ai'e 

 formed by the temperature of the aii* being much 

 below that of the earth, and consequently condensing 

 its watery exhalations. The greater the difference 

 of temperature, the denser is the mist, the condensa- 

 tion being more complete. 



I will observe, as on a former occasion, that the 

 time will probably anive when gi'eater precision will 

 be attained as to the time when om' various seeds 

 may best be committed to the soil. We shall owe 

 that advance to a more complete knowledge of what 



