CONIFERALES 



271 



others the roots are triarch; in and Pinus edidis, tetrarch. In ad- 

 ventitious roots of Taxodium imbricarium, the pentarch condition 

 is common; but even in the same cluster of roots, some are Hkely to 

 be tetrach, some, triarch, and many, diarch. 



Fig. 277. — Pinus cdiilis: transverse section of a young root after secondary growth 

 has become estabUshed. The outer part is scaUng off in plates. There is a resin duct op- 

 posite each of the four protoxylem points. The crushed protophloem is still visible, and 

 outside it are cells rich in starch, and just beneath the scaUng off layers are numerous 

 resin cells; X118. 



The protoxylem points, always exarch, appear early, and there 

 are indications of secondary development before the metaxylem 



