JOO Water 



same end. Our plants do not indeed go so far as to 

 drop their leaves altogether, but some of them do 

 greatly diminish both their number and size ; and some 

 clothe themselves with hairs, partly, as it would seem, 

 lest they should be deprived of too much moisture, 

 though partly also, probably, as a protection against 

 insects. An example or two of these must suffice, and 

 we will take, first, that of the Amphibious Persicaria — 

 a particularly interesting plant, as it grows both on 

 land and in water, and adapts itself to its situation in 

 a very marked manner. When it grows in water, 

 where, of course, it does not matter how much it may 

 lose, it has smooth, lance-shaped leaves ; but when it 

 grows on land the leaves are narrower, and not only 

 this, but they are covered as well with a quantity of 

 long hairs, pressed close upon the surface, which they 

 protect against evaporation. 



Then there is the Sweet Woodruff, whose lance- 

 shaped leaves grow in whorls of eight, for the plant 

 dwells in moist, shady places, where there is no risk in 

 having many leaves. But look from this to another 

 member of the family, the Quinsy Wort, and what do 

 we find ? The leaves are very narrow, and there are 

 but half as many of them. Why ? Because this little 

 plant grows on dry banks, where many and large 

 leaves would be dangerous to its welfare. 



It has been already mentioned that the Pine family, 

 which thrive in dry, sandy soils, have hard, needle-like 

 leaves, with few pores, and therefore give off but little 

 water, either by evaporation or transpiration ; and it is 

 for this reason that the air in a pine forest in summer 

 has none of the coolness which one finds in a forest of 

 what the Germans call ' leaf-treesV The ' needles ' of 



