PINE ROOT 249 



P. syhestris: mount some sections in glycerine, others 

 in chlor-zinc-iodine. Observe successively, starting from 

 the periphery of the section 



1. Withered remnants of the cortex : this may, 

 however, have been already completely thrown off. 



2. The pericycle, with its secondary products, con- 

 sisting of a thin external band of cork, the cells of 

 which are arranged in radial rows : within it is the 

 cork-cambium, having the same characters as above 

 described (p. 92) : internally will be found the re- 

 mainder of the original pericycle in a quiescent state. 



3. The phloem, forming, according to the age of the 

 root, a more or less complete ring. The constituents 

 resemble those of the phloem of the stem, and are often 

 distorted by pressure of the external tissues. 



4. The cambium, as in the stem. 



5. The xylem, in which may be recognized, near the 

 centre 



a. The groups of primary xylem, arranged in the 

 form of a Y, and each having, as before, a resin-passage in 

 the fork : the number of these is usually three (triarch), 

 or four (tetrarch). 



b. The masses of secondary xylem, more or less 

 fan-shaped, and alternating in position with the groups 

 of primary xylem. The number of the latter, and of 

 the masses of secondary xylem, varies in the lateral 

 root, four being the average number. The constituents 

 of the secondary xylem resemble those of the stem in 

 structure and arrangement. 



IV. Cut, and mount as before, transverse sections of 

 a root about one-eighth of an inch in diameter. 



The arrangement of tissues will be as before, but the 



