SCARLET RUNNER. 



Single cells will be seen to have grown out perpendicu- 

 larly to the surface as root-hairs. 



II. Cut sections successively at older points in the 

 same root,- 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 pri- 

 mary xylem : this explains their arrangement in four 

 rows as above observed with the naked eye. 



Z>. The pericambium, bundle-sheath, 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. 



This mode of origin of the lateral roots is the rule in the plants 

 with apical meristem, arranged according to Type II. (cf. infra, 

 p. 104). In the plants whose root-apex follows Type I. the lateral 

 roots are mainly, or even entirely, derived from the pericambium. 



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

 more from the apex, taking care to avoid the lateral 

 roots : 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 recognised. Observe espe- 

 cially 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. Cat transverse sections of an old root of the 

 Scarlet-Runner, and treat as before. Observe 



1. Centrally a parenchymatous Pith, relatively to 

 which 



