136 Roots 



but keep a close grasp of it, lining the worm- 

 burrows with thread-like fibres, which cling fast to 

 the sides. 



Roots coming in contact with a piece of limestone 

 will leave upon it a perfect impression of themselves, 

 even to the hairs with which they are fringed, showing 

 how, like the lichens, they have eaten their way into , 

 the solid substance. 



How do they do it ? We can hardly do more than 

 conjecture ; but it seems probable that the acid in the 

 roots acts much as acid contained in a bladder would. 

 If a glass tube is filled with water made slightly acid 

 with vinegar, and then covered with a piece of 

 moistened bladder strained tightly over the mouth, 

 and in contact with the liquid, this will represent the 

 root, though the resemblance would, of course, be 

 closer if the tube itself were of bladder. This, how- 

 ever, seems to be the only practicable way of trying 

 the experiment. The acid is very weak, as the acid in 

 the roots is weak ; but if salts, such as phosphate of 

 lime, and others found in the soil, are now strewn 

 upon the bladder, they will in a short time begin to 

 pass through it into the tube, being dissolved by the 

 weak acid in its pores. 



The acid in the roots acts, it is supposed, in a 

 similar way, and thus the dissolved minerals are 

 BUcked in. But, as before said, living things have 

 more power than dead ones ; so it may well be that 

 roots, like lichens, dissolve more than the weak acid 

 alone would do. , 



The roots take up what they themselves dissolve 

 from the particles of soil immediately surrounding and 

 closely touching them, and also what the water in the 



