Page:An introduction to physiological and systematical botany (1st edition).djvu/217

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187
PERSPIRATION OF LEAVES.

perspiration, but all proving it to be considerable. Evergreens are found to perspire much less than other shrubs.

The state of the atmosphere has a great effect on the rapidity of this perspiration. Practical botanists know how much sooner plants fade, and haymakers experience 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. 113. Succulent plants, destined to inhabit sunny rocks, or sandy deserts, imbibe with the greatest facility, 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, p. 68, has a thin dry leaf, capable of holding very little moisture.