44 THE WORK OF THE ROOTS [chap. 



by the roots of any crop occupying the soil in which 

 tlie manure is buried. 



Of the power of roots to anchor plants and hold them 

 firmly in position little demonstration is needed, but it 

 is interesting to see how many plants actually pull their 

 crown closer into the ground by contracting their roots. 

 Examine the young dandelions or plantains which have 

 established themselves on a lawn ; not only is there no 

 stem lifting the crown of leaves out of the ground, but 

 on the contrary this crown is pressed down tightly into 

 the ground. As a matter of fact it has been pulled 

 down by the contraction of the main root ; and if this 

 main root is carefully dug up in the early summer, 

 washed and examined, it will be seen to be corrugated 

 and to possess ridges showing where the contraction 

 has taken place. The crocus affords another interesting 

 example of contractile roots ; each year the new crocus 

 corm is formed on the top of the old one, so that after a 

 few years the corm would find itself on the surface of 

 the soil. However, the new corm develops a ring of 

 fleshy contractile roots which draw it down again into 

 the position occupied by the old one before its decay. 

 The seedling tubers of the Common Arum (Cuckoo-pint, 

 or Lords-and-ladies) possess similar contractile roots 

 which operate each season until the tuber has been 

 drawn down to its proper level. The habit of many 

 plants of throwing out adventitious roots from another 

 part of the stem than that from which the original roots 

 start should be observed ; in the case of cereals this 

 throwing out of adventitious roots from a point close to 

 the surface of the ground, much higher up than the 

 original crown of roots from the embryo, is a very 

 important factor in supporting the straw; like the 

 formation of side shoots, or " tillering," it is promoted 

 by free exposure to light and air. 



