HORSE-CHESTNUT ROOT 153 



of the layer of cork from the pericycle beneath them, 

 which thus cuts them off from a physiological connection 

 with the central cylinder. (Compare Fig. 10, p. 156.) 



For comparison with the above, and especially with 

 regard to the broad primary medullary rays, sections 

 should be cut of old roots of Cucurbita, and of the 

 common Nettle, both of which show parenchymatous 

 rays of large size. 



Comparisons should also be made of transverse 

 sections of the root of the Radish, the secondary tissues 

 of which consist chiefly of parenchyma with the vascular 

 elements scattered through it in small groups. 



ii. Ligneous Type. 



For comparison with the root of Pkaseolus, which is 

 characteristic rather of that of herbaceous plants, ob- 

 servations should also be made on the roots of some 

 woody plant. The root of the Elm has its cortex 

 densely crowded with mucilage-cells, and in other re- 

 spects is not very suitable for work : the Horse-Chestnut 

 (dEsculus Hippocastanum) is a better type of a root of 

 an arboreous plant. Dig up roots of this plant carefully 

 so as not to break off the finer fibrils : wash them 

 gently from the soil, and observe the reddish-brown 

 colour of the thicker and more mature parts, while the 

 ends of the thinner fibrils are pale-coloured. Note 

 also on passing from young portions to the older that 

 an outer coating of effete brown tissue is thrown off, 

 and thereby the bulk of the root may be apparently 

 diminished ; this is the cortex, which here, as in other 



