106 



A. H. Graves, 



A cross section of the coleorrhiza as represented in Text-tig. 23 

 shows that it is composed principally of a single cell-layer. The 

 section was cut purposely near the junction of root with stem, in 

 order to show how toward the proximal end of the coleorrhiza a few 

 of the cells of the subepidermal layer enter into its composition. 



As is shown by 

 longitudinal sec- 

 tions, the cells in the 

 outer or more distal 

 region of this sub- 

 jacent layer are un- 

 doubtedly the re- 

 sults of divisions 

 similar to those 

 which take place in 

 the epidermal or 

 coleorrhizal layer, 

 but at the proximal or basal part of this subjacent layer the cells 

 are larger and two or three rows deep, and those immediately adja- 

 cent to the root are considerably flattened. In this region, there- 

 fore, the subepidermal layers of the coleorrhiza are derived im- 

 mediately from the cells of the stem without division, being forced 

 outward by the development of the root and coleorrhiza. 



Wf^^i 



!Figure 23. — Portion of cross section of root show- 

 ing surrounding- coleoiTliizal layer, x 400. 



.-0Q1 



Figure 24. — Pliotomicrograph of longitudinal section of young 

 root still enclosed in coleoiTiiiza ; col, coleorrhiza ; r, root, x 50. 



PI. VII, fig. 38 shows a weU advanced stage, where by^ pressing 

 with the cover Mass the root was detached from its connection 



