SENSIBLE PERSPIRATION. 143 



rapidity of this perspiration. Practical botanists know 

 how much sooner plants fade, and haymakers expe- 

 rience how much faster their work is done, some days 

 than others, and those days are by no means always 

 the most sunny. In a hot dry day plants are often 

 exhausted, so as to droop very much towards evening, 

 especially in the dry unsheltered bed of a garden. Such 

 as have fleshy roots, indeed, have a singular power of 

 resisting drought, which has already been explained, 

 p, 87. Succulent plants, destined to inhabit sunny 

 rocks, or sandy deserts, imbibe with the greatest faci- 

 lity, and perspire very sparingly. Evergreens are not 

 generally very succulent, but their cuticle appears to be 

 constructed like that of succulent plants, so as to allow 

 of little evaporation. The Cornelian Cherry, whose 

 immense perspiration we have recorded, /;. 52, has a 

 thin dry leaf, capable of holding very little moisture. 



The nature of the liquor perspired has been already 

 noticed, p. 5%. In hot weather it has been observed 

 by Hales, Du Hamel and Guettard, to partake occa- 

 sionally of the peculiar scent of the plant that yields 

 it ; but in general the odorous matter is of too oily a 

 nature to be combined with it. 



The sensible perspiration of plants is of various 

 kinds. When watery, it can be considered only as a 

 condensation of their insensible evaporation, perhaps 

 from some sudden change in the atmosphere. Groves 

 of Poplar or Willow exhibit this phenomenon, even 

 in England, in hot calm weather, when drops of clear 



