io 4 PRACTICAL BOTANY 



ROOT 



I. Cut transverse sections of the root of the Maize, selecting 

 a well-grown, underground piece of root : mount in glycerine, 

 and examine first under a low power, then under a high power. 

 Starting from the periphery observe 



1. The superficial piliferous layer, consisting of small cells, 

 many of which have grown out into long root-hairs. 



2. Immediately below this is a protective layer of exodermis, 

 with more or less cuticularized cell-walls. 



3. The cortical parenchyma, a broad band, of 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-looking 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 surrounding a vessel or 

 vessels. 



