SCARLET RUNNER -ROOT 87 



6. The parenchymatous cortex, a thick band of tissue, with 

 intercellular spaces, and 



7. The piliferous layer, a single superficial layer, not well 

 marked. Single cells of this layer will be seen to have grown 

 out perpendicularly to the surface as root-hairs, which as a 

 rule are not branched, and are of cylindrical form, with thin 

 cell-walls : particles of soil may be found attached to many of 

 them. 



II. Cut sections successively at older points in the same 

 root, treat as before, and observe the mode of origin of 

 the lateral roots, noting more especially the following 

 facts : 



a. The lateral roots arise opposite the groups of primary 

 xylem : this explains their arrangement in four rows as above 

 observed with the naked eye, since the number of groups of 

 primary xylem is usually four. 



b. The pericycle, endodermis, and a small portion of the 

 cortex, all take part in their formation. 



c. In the older lateral roots it may be seen that their vascular 

 system is continuous with that of the main root. 



d. The lateral roots, increasing in length, burst through the 

 outer layers of cortex and the piliferous layer : since they 

 originate from deeply seated tissues and rupture the more 

 superficial ones, they are said to be of endogenous origin. 



III. Cut transverse sections of the root, six inches or more 

 from the apex, avoiding the lateral roots : take care also to avoid 

 the thick base of the hypocotyledonary stem, which shows a 

 structure characteristic neither of the stem nor of the root : 

 treat as before. 



The general arrangement of tissues is the same 'as has been 

 above described, though there has been increase in bulk, and 

 the xylem and phloem, being now more fully developed, are 

 more easily recognized. Observe especially that the parenchyma, 

 lying centrally to the phloem, has begun to divide repeatedly 

 by tangential walls : in fact, four cambium bands are thus 

 formed, from which is derived the secondary thickening of 

 the root. 



IV. Cut transverse sections of an old root of the Scarlet- 



