66 



ROOT-HAIRS 



The general structure of the root can best be studied in a 

 cross-section through the mature region, the Creeping Buttercup 

 (Ranunculus repens) furnishing , suitable material fora first ex- 

 ample. Under the low power of the microscope the broad paren- 

 chymatous cortex (Fig. 27, C.), whose cells contain numerous 

 starch-grains (s.), and the central conducting strand, are again 



FIG. 27. Transverse section of the central part of the root of the Creeping 

 Buttercup (Ranunculus repens}. The walls of the xylem elements are 

 shown black. C., inner part of cortex ; ca., cambium ; ex., companion 

 cell ; en., endodermis ; i.p., intercellular spaces ; p., pericycle ; 

 pt.xy., protoxylem ; s., starch ; s.t., sieve-tube. 



sharply contrasted. At the edge of the section is a layer of 

 shrunken cells (Fig. 28, r.), some of which are prolonged into 

 shrivelled root-hairs. This epidermis withers above the zone 

 of root-hairs and, since its chief function is their production, 

 it is more usually termed the piliferous layer. It is only in 

 sections cut nearer the growing tip that its cells are as yet un- 

 contracted, and can be seen to form a single layer. 



The root-hairs, each arising from a separate cell (Fig. 28, r.), 



