140 



THE GREEN-HOUSE. 



soon as poured on it, and the soil at that moment may 

 be said to be left in a state favourable for vegetation ; 

 but as the evaporation from the surface and sides of 

 the pot, and the transpiration of the plant go on, it 

 becomes gradually less and less so, and if not soon 

 re-supplied, the earth would become dry and the plant 

 shrivelled and liable to die, either from the w^ant of 

 vrater, or its sudden application. Thus the roots of 

 a plant in a pot surrounded by air, such as the pots 

 on a green-house stage, are liable to be alternately 

 chilled and scorched by cold or heat, and deluged or 

 dried up by superabundance or deficiency of vi^ater, 

 nothing but the unceasing care and attention of the 

 gardener to lessen the tendencies to these extremes, 

 would at all preserve the plant from destruction. 

 Hence the advantage of plunging pots in sand, ashes, 

 earth, saw-dust, tan, or any porous non-conductor; 

 and also of shading them by leaves, straw, or moss ; 

 or, where this cannot be done, placing them on cool 

 stone platforms, which do not admit air from below 

 like open gradations of shelves, 



A careful imitation of nature is not always the 

 proper mode of treating plants in a state of art. It is 

 obviously erroneous when applied to plants of culture, 

 as to most culinary plants and fruit trees ; but cor- 

 rect when applied to plants of fixed habits, as heaths, 

 or plants whose characters and habits in a wild state 

 it is desirable to preserve ; as for example medical 

 plants, which are all rendered less efficacious in pro- 

 portion as they are affected by culture. 



