3 8 THE WHEAT PLANT 



lateral axes appear, four or five roots being usually present at this time at 

 the tillering node, the longest being about 3 inches, the shortest about 

 ii inches long, the primary shoot then showing 4 or 5 leaf-blades, the two 

 secondary shoots 3 or 4 blades each. For a considerable period these 

 roots are unbranched, and clothed throughout their entire length except 

 the tip by root-hairs. Later, numerous branches appear, after which 

 time the piliferous layer shrivels and the roots become thinner and brown. 

 New roots continue to break out from the nodes of the straws until May 

 or June, by which time an extensive system has been established in plants 

 which are not crowded. All these adventitious 

 roots are of greater length and thickness than 

 the seminal roots ; some, which spring from 

 near the base of the straws, are 1-5-2 mm. in 

 diameter, and ultimately become very rigid in 

 the first inch or so of their lengths ; in the 



FIG. 24. Arrangement of the adventitious 

 roots at the three basal nodes of a culm 

 (xi'S). i, Front ; 2, side view; 3, 

 transverse sections at a and b. 



FIG. 25. "Anchoring "roots 

 at the base of a culm (nat. 

 size). 



parts exposed to the air, chloroplasts are present in their cortical tissues 

 (c, Fig. 30). About 60 per cent of the roots are found in the upper 8-12 

 inches of the soil, the rest extend to greater depths, a few occasionally pene- 

 trating 4 or 5 feet or more, especially in deep loams. 



The root-system of thin-strawed varieties with upright young shoots 

 is less extensive than that of thick-strawed forms with a spreading habit 

 when young. 



Moreover, the roots of wheats with erect young shoots are thin and 

 spread very little near the surface of the soil ; plants with roots of this 

 habit are easily laid by wind and rain. 



The roots of the varieties with young spreading shoots are stout ; 

 they also make a wide angle with the vertical and anchor the plant firmly 

 to the soil, isolated and normally grown plants of these varieties being 

 never laid by wind or rain. 



