180 FERSPIRATION OF LEAVES. 



damp cellar, or immersed in water, the leaves 

 revive, by which their power of absorption is 

 also proved. Hence the use of a tin box to 

 travelling botanists, for the purpose of re- 

 {?training the evaporation of plants, and so 

 preserving them fresh for some days till they 

 can be examined, as well as of reviving faded 

 plants, if the inside of the box be moistened 

 before they are shut up in it. 



Dr. Hales found that a plant of the Great 

 Annual Sunflower, Helianthus aimuus, lost 

 1 lb. 14 oz, weight in the course of twelve 

 hours in a hot dry day. In a dry night it 

 lost about 3 oz.; in a moist night scarcely 

 any alteration was observable, but in a rainy 

 night it gained 2 or 3 oz. The surface of 

 the plant compared with that of its roots 

 was, as nearly as could be calculated, in the 

 proportion of five to two ; therefore the roots 

 must have imbibed moisture from the earth 

 of the pot in which the plant grew, and which 

 was all previously weighed, in the same pro- 

 portion of five to two, otherwise the leaves 

 would have faded. The same experiment 

 was made on the Vine, the Cabbage, &c., 

 with various results as to the exact degree of 

 3 



