THOSE LITTLE WORKSHOPS 91 



a man really transpires, as well as a tree. All day long 

 water- vapour is escaping through the pores of his skin 

 — about as much as one pint in twenty-four hours. This 

 is sometimes called " insensible perspiration," because 

 we do not see or feel it. 



Plenty of water, as you now know, taken in by the 

 roots, mounts upward by way of the tree-trunk into 

 the leaves. And in each drop there may be, at the 

 least, a few specks of some other kind of substance, 

 needed by the tree. 



Such tiny specks ! — the very smallest that we can 

 imagine ! — so minute, so light, that they float in the 

 water unseen, and can pass with it through the delicate 

 skins of the cells and tubes. Yet, tiny though they 

 are, the tree must have them, if it is to carry on its work. 



As they pass they are caught hold of and kept back 

 and made use of by the leaves. And all the water that 

 is not wanted is sent on to the leaf-pores, to escape as 

 vapour into the outside air. 



This is yet another work done by the leaves. Not 

 only do they help to make the air more pure, but also 

 they help to keep it well supplied with moisture. Here, 

 too, we have to do with large quantities. Immense 

 amounts of water travel thus, from the soil upwards 

 through the tree-trunks, then out by way of the tiny 

 leaf-pores, into the air which we breathe. 



It has been reckoned that a well-grown Apple-tree, 

 in the course of a single spring and summer, may part 

 with something like two hundred and fifty pounds' 

 weight of water. If we count the trees growing in one 

 large orchard, we can soon find out how many tons of 

 water are poured through them in a year. The total 



