POTAMOGETONACEAE 



[CH. 



end 



C D 



FIG. 40. Reduction series in central cylinder of stem in Potamogeton. A, P. 

 crispus, L. (cf. diagrammatic Fig. 39, C) (x 160) ;'B, P. lucens, L., in which fusion of 

 the strands has gone further, so that each of the three bundle groups has one 

 xylem only; mp = conjunctive tissue (xi3o); C, P. pusillus, L., in which the 

 xylems of all the individual bundles form a single central passage ( x 290) ; D, P. 

 pectinatus, L., completely concentric structure in which all trace of the component 

 bundles is lost; end = endodermis (x29o). [Schenck, H. (1886).] 



