SOILS PECULIAR TO PLANTS. 529 



jetable life except clay, lime, and sand, with the aid of water 

 i the gaseous matters of the atmosphere. Those gaseous 

 tters are nitrogen, brought to the land by rain, in the form 

 ammonia, or of nitric acid (see page 39), and carbonic 

 d, or other gaseous forms of carbon. Phosphoric acid and 

 phur seem to be sufficiently abundant in all sand or clay 

 enable plants to exist at least, if not to grow in them with 

 [our ; for although chemists, in their analyses, report in some 

 ies only a trace of such substances, yet it must be remem- 

 ced that, as Dr. Daubeny has remarked, if only -j-owoth 

 ft may be present in a given sample of soil, yet even that 

 )resents more than 350lbs. as existing in the soil of an acre 

 ivn to the depth of a foot, 

 ^at the gardener tries to imitate is the soil in which plants 



I naturally found in the greatest vigour. "When he learns 

 it the pedunculate Oak always thrives best in strong clay, he 

 ers that heavy clay is necessary to that kind of tree. If he 

 IS that the Box-tree delights in chalky hiUs, and the Saint- 



II in chalky fields, he is justified in considering that cal- 

 •eous land is what they each prefer ; and when he knows 

 it fibrous-rooted plants, like Khododendrons and Heaths, 

 Irish wherever peat and sand occur, he has recourse to 

 it and sand for their cultivation. Nor is he to be censured 



this. On the contrary; even if his conviction that the 

 Is in which plants grow wild are what suits them best should 



theoretically wrong, he at least knows that it is practically 

 ht ; and that if following nature closely shall not lead to the 

 3t possible results, it is sure not to lead bim astray, provided 

 has the skill to interpret natural phenomena with accuracy. 

 It is probable, however, that the influence exercised by soil 

 on vegetation is due as much to its physical conditions as 

 its chemical nature. At all events, I entertain no doubt 

 it the former have been too much lost sight of in the search 



chemical evidence ; and that in gardening, which is always 

 cultivation of fertile soils, it is the subject which most 

 Bands attention. Soil, considered without reference to the 

 janizable substances it contains, appears to act upon plants 

 lefly by its power of absorbing and parting with heat and 



