ROOTS 27 



some of the drier parts of California wheat roots have been 

 known to grow to a depth of 15 feet and the roots of the 

 California poppy to a depth of 13 feet. Eoots may penetrate 

 to much greater depths, those of the mesquite of the South- 

 western States and Mexico sometimes descending to reach 

 water as much as 60 feet. It is not difficult to get an idea of 

 the extent of the root system of such a plant as Indian corn. 

 Carefully dig away the earth from one side of the plant at a 

 distance of about two feet, keeping a constant lookout for 

 smaller rootlets. If none are found, extend a trench com- 

 pletely about the plant at the distance already used as a 

 radius. Make the trench about two feet deep and stand a 

 piece of poultry netting in it, so as to make a circular fence 

 about the roots of the plant. Run some wire stakes crosswise 

 through the mass of roots, so as to reach across its entire 

 diameter. With a stream of water from a garden hose or with 

 numerous pails of water wash away the earth as completely 

 as possible from the mass of roots and remove the root system 

 entire. It may then be used for illustration in the schoolroom. 

 28. Pull exerted by roots. After root fibers or the taproots 

 of herbaceous plants have attained their full length, in many 

 kinds of plants a decided shortening of the root takes place. 

 This shortening originates in the cellular portion of the cor- 

 tex, between its outer layers and the central cylinder of the 

 root, and it may amount to from 10 to 25 per cent of the 

 length of the root before contraction. Because the epidermis 

 does not contract, its outer surface often becomes much wrin- 

 kled, especially in the roots of bulbous plants. The shorten- 

 ing of the fibrous roots which spring from a taproot holds it 

 firmly in place, as a derrick is held upright by guy ropes. 

 Sometimes, as in the dandelion, the taproot shortens about 

 as fast as the short stems which crown the root grow upward. 

 In this way the rosette of leaves is kept firmly pressed against 

 the ground, or it may even be drawn slightly into the earth. 

 Grass plants on a lawn are injured or destroyed by being de- 

 prived of light by the rosette of dandelion or fall dandelion. 



