CH. II.] THE ROOTS. 67 



usually annually renewed, and the caudex (or main 

 limb of the root) extended in length : by these means 

 they each year shoot forth into a fresh soil, always 

 changing their du'ection to where most food is to be 

 obtained. If the extremity of a root is cut off, it 

 ceases to increase in length, but enlarges its circle of 

 extension by lateral shoots. 



The distance to which the roots of a plant extend 

 is much greater than is usually imagined; and one 

 reason of the stunted growth of plants in a poor soil 

 is, that the sap collected and elaborated by them has 

 to be expended in the extension of the roots, which 

 have to be larger in proportion as the pasturage near 

 home is scanty. An acorn accidentally deposited on 

 a wall produced a young oak ; but this made no pro- 

 gress until its root had descended the whole height 

 of the wall, and had penetrated the soil at its base. 



In deep, poor siliceous soils I have traced the roots 

 of trees from twelve to fourteen feet perpendicidar 

 without reaching their tennination. Those of the 

 Canada thistle, seven feet ; common fern, eight feet ; 

 wheat, thirty inches; oats, twenty-four inches; 

 potatoes, eighteen inches ; onions, twenty inches ; 

 caiTots, parsnips, and beet, two feet. The distance 

 to wliich roots will travel, and their tenacity of life, 

 render them, often, veiy obnoxious to the gardener. 

 Thus the common couch_grass (TriUcum rej)jim^)-is — ■' 

 the most troublesome of weeds, for every fragment of 



F 2 



