94 THE WORLD'S LUMBER ROOM. 



more mineral matter in proportion to their size than any 

 others, still, all plants contain some acid, and all, on being 

 burnt, yield a certain quantity of ash, some more, some less, 

 which they have absorbed from the soil and could not have 

 done except in the form of liquid. 



We have already seen something of the solvent powers 

 of carbonic acid, and this gas plants are constantly giving 

 off through their roots, which are much more numerous than 

 people generally have any idea of. Rye, beans, and peas, 

 for instance, will send down a thick mat of white fibres to a 

 depth of four feet ; winter wheat has been known to send 

 out roots seven feet long in forty-seven days, while clover a 

 year old has roots three feet and a half long. 



But this is not all. Besides these obvious roots, there are 

 very many others so fine and hair-like that they escape notice 

 altogether. Yet the plant takes up its nourishment through 

 all and especially through these young, almost invisible 

 roots (Fig. 20). 



By way of experiment t beans, maize, and wheat, have 

 been planted in fine quartz sand, having at the bottom plates 

 of marble (carbonate of lime), magnesian limestone (car- 

 bonate of lime and magnesia), gypsum (sulphate of lime), and 

 glass. 



Being kept well watered, the seeds soon began to sprout 

 and send out roots, and when they had reached the plates 

 below and could get no farther, they spread themselves out 

 horizontally. 



When the plates were examined after a time, the marble 

 and magnesian limestone were found to be corroded eaten 

 into by the roots, the impression of even the root-hairs being 



