THE ROOT 



157 



Fig. 113 shows the central region of the root under a higher degree of 

 magnification, and the arrangements described above now become 

 much more clearly visible. Another structural feature now for the 

 first time presents itself namely, the presence of groups of small- 

 sized elements of the primary xylem in alternation with the more 



FIG. 113. Part of same, more highly magnified 



pronounced radial bands of secondary wood and phloem. The 

 protoxylem groups are incompletely united in the center, and 

 a pithlike cluster of parenchymatous cells is consequently found 

 in the midst of the primary wood, a condition quite frequently 

 present both' in herbaceous dicotyledons and generally in the 

 monocotyledons. In the woody dicotyledons and in the conifers 

 a structure comparable to the pith of the stem is ordinarily absent 

 in the root. 



