HYACINTH ROOT 181 



which the peripheral part is often sclerenchymatous, 

 and this is especially the case in the aerial prop-roots : 

 observe the regularity of arrangement of the inner 

 part of the cortex, of which the innermost layer is to 

 be recognized as 



4. The endodermis : the cell-walls of this layer are 

 in old roots thickened on three sides, the outer wall 

 remaining thin, and the radial walls in young roots 

 show the usual dark dotted appearance. 



5. Within this is the pericycle, a layer of cells with 

 walls thin when young, but they may be lignified when 

 old : the series is interrupted opposite the xylem 

 masses, which abut directly on the endodermis. 



6. The vascular cylinder, round the periphery of 

 which are disposed 



A. Xylem -tissues, recognized by their dark-look- 

 ing lignified walls, especially those of the large vessels 

 these lie nearer the centre, while the smaller elements 

 of the protoxylem are at the extreme periphery. 



B. Phloem-tissues, which alternate with the 

 xylem-groups, and are to be recognized by their brighter 

 cellulose walls. Note that the number of xylem and 

 phloem groups may vary, and is often very large. 



7. Centrally lies a bulky pith, in which may be seen 

 one or more irregular groups of sclerenchyma surround- 

 ing a vessel or vessels. 



II. Cut transverse sections of the root of Hyacin- 

 thus orientalis. An old root must be taken, and the 

 sections should be cut as far as possible from the apex. 

 Treat them with potash, and mount in glycerine. 

 Starting from the outside, note successively 



1. The superficial piliferous layer, single cells of 





