HORSE-CHESTNUTROOT 89 



the older that an outer coating of effete brown tissue is thrown 

 off, and thereby the bulk of the root may be apparently dimin- 

 ished ; this is the cortex, which here, as in other cases, is only 

 a temporary covering of the younger portion of the root. The 

 soil will be found in this case also adherent to the fibrils, thus 

 indicating the presence of root-hairs at some distance from the 

 apex, but not at the extreme apex, nor on the older portion of 

 the root where the cortex has been thrown off. 



V. Select a strong young fibril : embed a short piece of it, 

 taken about half-way between the apex and the beginning of 

 the red colouring : cut transverse sections, and clear with 

 potash, or " eau de javelle " : mount in glycerine, and examine 

 under a high power : observe 



1 . The pilif erous layer, a rather irregular layer with slightly 

 thickened outer wall : single cells may have developed as 

 root-hairs. 



2. The exodermis showing a thickening of the radial walls 

 not unlike that common in endodermis : this thickening is 

 continued all round the anticlinal walls, and is not uncommon 

 in roots of woody plants. 



3. A broad band of ordinary cortex, with large intercellular 

 spaces : the walls are more thickened nearer the central 

 cylinder, and are pitted. 



4. The endodermis or bundle-sheath, with the characteristic 

 dot on the radial walls : within this is the central cylinder, 

 composed of 



5. A peripheral layer of the pericycle : occasional periclinal 

 divisions may be seen in the cells of this layer. 



6. The groups of primary xylem usually four in number 

 which will be still separate from one another, or, according to 

 the age of the root, may be united at the centre : note the 

 details of appearance of this primary xylem, so as to be able to 

 recognize it in the older roots. 



7. The groups of primary phloem, equalling in number those 

 of the xylem : this tissue is not well marked. 



8. Narrow bands of parenchyma separating the successive 

 groups of phloem and xylem : subsequently these cells are the 

 seat of origin of the cambium. 



