SOWING. 23 



depth will be found to range similarly above the at- 

 mospheric temperatiu'e. There is no doubt that in 

 tropical climates, the bare exposed soil becomes heated, 

 for a few inches in depth, to a degree higher than 

 that of the air incumbent upon it. But this is not the 

 case about the roots of plants ; for their fohage, and 

 the herbage naturally clothing the soil, preserve this 

 from such a pernicious elevation of temperature. That 

 such an excessive elevation is injmious, is known to 

 every obseiTer of plants, whether the plants are grow- 

 ing in the tropics or in a stove. The roots are stimu- 

 lated to imbibe moisture faster than the foliage can 

 digest sufficiently the sap thus forced to them, and 

 that foliage is expanded wider and more weakly m 

 the vain effort to keep pace with the supply. This is 

 only one among many instances of that property, so 

 wisely given to organised beings by their Creator, of 

 adapting themselves to circumstances ; and it is only 

 when the vicissitudes of those circumstances are too 

 violent, or too long continued, that they fail in their 

 effort at conformity. 



If the temperature of the soil be unnaturally below 

 that in which the branches are vegetating, the effects 

 are equally, though differently, disastrous. The sup- 

 ply of sap is too much diminished in quantity, and 

 the edges of the leaves consequently die, or the blos- 

 soms fall, or disease attacks some part of the fruit, 

 according to the nature of the plant, or the stage of 



