144 THE GREENWOOD TREE. 



so I will say here at once, without further ado the 

 plant requires drink as well as food, and the roots are 

 the mouths that supply it with water. They also suck 

 up a few other things as well, which are necessary 

 indeed, but far from forming the bulk of the nutriment. 

 Many plants, however, don't need any roots at all, 

 while none can get on without leaves as mouths and 

 stomachs. That is to say, no true plantlike plants, for 

 some parasitic plants are practically, to all intents and 

 purposes, animals. To put it briefly, every plant has 

 one set of aerial mouths to suck in carbon, and many 

 plants have another set of subterranean mouths as well, 

 to suck up water and mineral constituents. 



Have you ever grown mustard and cress in the 

 window on a piece of flannel? If so, that's a capital 

 practical example of the comparative unimportance of 

 soil, except as a means of supplying moisture. You put 

 your flannel in a soup-plate by the dining-room window ; 

 you keep it well wet, and you lay the seeds of the cress 

 on top of it. The young plants, being supplied with 

 water by their roots, and with carbon by the air around, 

 have all the little they need below, and grow and thrive 

 in these conditions wonderfully. But if you were to 

 cover them up with an air-tight glass case, so as to 

 exclude fresh air, they'd shrivel up at once for want of 

 carbon, which is their solid food, as water is their 

 liquid. 



The way the plant really eats is little known to 

 gardeners, but very interesting. All over the lower 

 surface of the green leaf lie scattered dozens of tiny 

 mouths or apertures, each of them guarded by two small 



