Water 103 



large leaves, has a considerable surface exposed to sun 

 and air ; and so with other conspicuously large-leaved 

 plants. But when, instead of a few large leaves, a 

 plant has many small ones, it is not so easy to realize 

 what the whole surface may amount to. 



A sun-flower, for instance, has leaves of a good size, 

 and yet it is rather surprising to find that in a plant 

 only three feet and a half high, the whole leaf-surface 

 may amount to more than thirty-two square feet ! 

 One specimen of this size was found to give up from a 

 pint to a pint and a half of water during a day of twelve 

 hours. The sun-flower is quite outdone by the cabbage* 

 however, one specimen of which gave off nearly two 

 pints and a half in twenty-four hours, and that from 

 leaves which, had they been spread out, would have 

 covered only nineteen square feet. We have seen how 

 well the cabbage is protected by its wax coating against 

 evaporation, so that almost the whole of this amount 

 is given off by the plant's own action. The camellia is 

 much less thirsty; it has fewer pores, and its thick, 

 glossy leaves are so efficiently protected, that half an 

 ounce of water, ^ pint to the square foot of foliage, 

 was all that one plant gave up in a day and night. 



These calculations are comparatively simple; but, 

 when we come to trees, who would venture to guess at 

 the extent of surface exposed to the air and sun by the 

 leaves upon an elm? We look up at the quivering 

 multitudes, and feel as if it were hopeless for anyone 

 even to attempt to count them ; it is too bewildering ! 



Yet the calculation has been made, and the leaves 

 on a not very large elm-tree are said to be about 

 7,000,000, which would give a surface of about 200,000 

 square feet, or five acres ! 



