PHASEOLUS ROOT 149 



5. The primary root, on the upper part of which 

 are 



6. Numerous secondary or lateral roots. These 

 are formed in acropetal order, and are arranged in 

 regular longitudinal rows, usually four in number. On 

 the youngest part of the primary root (i.e. within three 

 inches or more of the apex) no lateral roots are to 

 be seen. 



Observe that particles of the sawdust, &c., adhere to 

 the older parts of the roots, while the younger apical 

 parts come out of the soil quite clean : this is due to 

 the fact that root-hairs are present on the older parts, 

 but not on the youngest parts close to the apex. 



Microscopic Observations. 



Harden the roots in alcohol for two or three days or 

 more. In order to cut the sections it will be necessary 

 to hold the roots between pieces of pith, or, better, to 

 embed in paraffin. 



I. Cut transverse sections of the primary root at a 

 point nearer the apex than the youngest lateral roots, 

 i.e. about two inches from the end : clear the sections 

 with weak potash, or " eau de javelle," and mount in 

 glycerine. 



Observe the following tissues : 



1. At the centre of the circular section is a mass of 

 parenchymatous pith. At the periphery of this are 



2. Radiating groups of elements of the primary 

 xylem, which are the most strongly marked tissues of 

 the young root. The number of these is most often 



