CHAPTER IV 



THE ROOTS 

 GENERAL MORPHOLOGY 



THE roots of the wheat plant may be divided into two groups, namely, 

 (i) the seminal roots, or those belonging initially to the embryo, or which 

 develop later from the hypocotyl or near it, and (2) the adventitious roots, 

 which spring from the nodes of the plant, within the soil or just above it. 



As previously mentioned, the embryo possesses five roots, namely, a 

 primary radicle and two pairs of lateral rootlets, which originate from the 

 hypocotyl in a plane parallel to the face of the scutellum ; a sixth is often 

 produced later from a point just behind the epiblast at the base of the 

 plumule, and grows out at right angles to the plane in which the others are 

 found (4, Fig. 18 ; n, Fig. 22). 



The primary radicle and the first pair of seminal rootlets burst through 

 the tissue of the coleorhiza soon after germination commences, these being 

 followed subsequently by a second pair ; the sixth rootlet, if it appears at 

 all, does so only after the others have attained a considerable length when 

 growth is more advanced. A third pair appears immediately above the 

 second pair and in the same plane, making in all eight seminal roots. 



The apex of each root is pointed, smooth, and more or less mucilagin- 

 ous. The growing point is protected by the root-cap, the outside of 

 which is continually being exfoliated as the tip of the root is forced through 

 the soil, and as rapidly renewed on the inside by the activity of its meristem. 



The surface of the rootlet for some distance behind the apex is clothed 

 with extremely delicate root-hairs. 



As the root increases in length and penetrates into fresh regions of the 

 soil, new root-hairs arise at a short distance from the tip, while those on 

 the older portions of the root, after collapsing, lose their absorptive power 

 and turn brown and die. The number of root-hairs is extraordinarily 

 large ; from 700 to 1000 or more per millimetre length of root are found in 

 the region of most active absorption. 



A number of hairs similar in form and function to root-hairs often 



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