124 HEAT AND MOISTURE. 



position will select situations most favorable for their supply and near 

 such waters as contain them. 



Heat and Moisture. 



The evidence of something like a bottom heat" in the greater 

 temperature of the soil over that of the atmosphere and the marked 

 vigor of plants growing near hot springs, or subterranean fires, may 

 have induced the practice of employing hot beds in cultivating delicate 

 plants and in producing valuable seeds. But this cannot be applied 

 beneficially by art when such plants are natives of colder climates. 

 The soil in which are to be raised tropical plants is to be permanently 

 elevated to at least 75 - 1 or the seeds will not germinate; or, if they do, 

 they present a sickly appearance. Hence they cannot germinate at 

 the ordinary temperature of our soil as it seldom rises, even for a 

 short time, above 65 P . But the intensity of bottom heat depends 

 nevertheless on the constitution or species of the plant and the known 

 temperature of its native climate, a little above which the heat should 

 doubtless be raised, in order to secure the original properties of the 

 plant. Hence the failure to raise successfully oranges in tubs when 

 the soil cannot be above 66 and in winter sinks to 36, while that o{ 

 the soil where they flourish is from 80 to 85 and never falls below 

 58. The same may be said in respect to the vine. The necessity of 

 the soil-temperature being above that of the atmosphere accounts for 

 the fact that ornamental trees in our parks and elsewhere, when 

 paving stones are placed around them, frequently die or fail to flour- 

 ish, because the earth, instead of being warmer, is thereby kept con- 

 stantly colder than the atmosphere. If the bark of a fruit tree be 

 stripped off in spring, while the bark is loose and a new layer of inner 

 bark is forming, and a frosty night or cold wind occurs, the inner bark 

 becomes again firmly attached ; and, although the tree may appear 

 healthy and sustain its foliage and blossoms, and its fruit set well, yet 

 nearly the whole falls off at the time its growth should commence. 



The, moisture and temperature of a soil, more than its mineralogical 

 character, is believed to determine vegetation. A distinguished gar- 

 dener soaks the roots of fruit trees in a mixture of equal parts of 

 boiling and cold water, and sprinkles the trees when necessary with 

 lukewarm water. This is attended with great success. The success 

 of the Dutch gardeners is also attributed to their application of heat 

 to the roots. Tan-bark beds are the usual source of bottom heat. 

 The importance of water in vegetation is that it supplies the plant 

 with the elements of its food and is the means by which the soluble 

 parts are conveyed into the system of plants. The object is to learn 

 the amount required and the periods at which it should be applied ; 

 plants evidently require an abundant supply during growth ; and in 



