THE BROAD BEAN PLANT. 5 



the parent-root at this point with a sharp knife or a razor, and ex- 

 amining with a lens the cut surface ? In what region of the main root 

 are the branches shortest and thinnest? Look for young branches just 

 emerging from the parent-root ; in what direction do they grow at first ? 



10. Root-Tip. Note the gradual tapering of the main axis and of 

 the rootlets towards their free ends, and the softness and whiteness of 

 the latter as compared with the older parts. Cut off the ends of some 

 of the rootlets, about an inch behind the extreme tip, place them in a 

 drop of water on a glass slide, and examine them with the lens ; try 

 holding the slide (1) against the light, (2) over a white surface, (3) over 

 a black surface. 



11. Root-Hairs. Look for very fine threads, which will be found 

 behind the root-tip, if the latter has not been damaged. These are 

 the root-hairs, to which small particles of soil may still be sticking. 

 Root-hairs are more easily seen in seedlings. They previously 

 existed on the older parts of the root, but they disappear as the root 

 grows, while new hairs are continually being formed just behind the 

 growing extremity of the rootlet. 



12. Root-Cap. At the end of each rootlet, note the more 

 transparent conical mass at the extreme tip, separated from the 

 denser main body of the rootlet by a curved outline. This conical 

 mass is the root-cap ; it is thickest at the tip and extends a little 

 distance at the sides, fitting over the end of the rootlet like a thimble 

 on a finger. 



Root-hairs and root-cap can be more easily examined in a seedling ; 

 they are often damaged in removing the mature plant from the soil. 



13. Root-Nodules. Note, here and there on the main root and 

 the rootlets, little wart-like swellings, varying in size and shape. These 

 swellings (nodules or tubercles) are characteristic of the roots of 

 Beans, Peas, Clover, and allied plants. See Art. 240. 



14. Hard and Soft Tissues of Root. Cut the main root and 

 the branches at several points, transversely and longitudinally, and note 

 the hard central part surrounded by the soft outer tissue. Scrape the 

 latter off, all round a piece of root, to see the hard central cylinder. Is the 

 hardness of this central tissue due to the presence of woody substance, 

 as in old roots as well as stems of trees ? It is easy to find out. Get 

 some aniline chloride (about l^d. per ounce), dissolve in a little alcohol, 

 and add water to make a 10 per cent, solution. Dip a wooden match 

 into the solution : does the match turn bright yellow when withdrawn ? 

 If the colour does not appear quickly, add a few drops of hydrochloric 

 acid to the solution. This solution affords a ready test for woody 

 substance (lignin). Place some on your sections of the root, and notice 

 which parts turn yellow. 



