CH. IV.] THE LEAVES. 141 



sandy, exposed soils, have, on the other hand, either 

 fewer or smaller stromates. Criniim amahile, an in- 

 habitant of swamps near Calcutta, has 40,000 of the 

 largest known stromates on ever}^ square inch of its 

 leaves ; whilst an aloe from the exposed sands of the 

 Cape of Good Hope, has 45,000 of the smallest, and 

 not equal in transpiring power to half the same num- 

 ber of stromates in the leaves of the Crinum. I 

 have not been able to test their relative transpiring 

 powers ; but of two similarly constnicted plants, of 

 nearly similar size, the rate of perspiring in July, 

 both in a temperature of 65°, but not exposed to the 

 sunshine, was as follows. In six hours, Mesemhry- 

 anthemum Deltoides, native of an arid soil, exhaled 

 eight grains, whilst Caltha palustris, found only in 

 marshy places, exhaled twenty-five grains. In the 

 absence of certain information, therefore, the gardener 

 may conclude, as a guide for his treatment of a new 

 plant, that, if its stromates are large, it will require 

 abundance of water. 



Another circumstance most influential in control- 

 ing the transpiration of plants, is the hygrometric 

 state of the atmosphere in which they are growing. 

 The drier the air, the greater is the amount of 

 moisture transpired ; and this becomes so excessive, 

 if it be also promoted by a high temperatui'e, that 

 plants in hothouses, where it has occui'red, often djj 

 up as if burned. The justly-lamented Mr. Daniell 



