64 



POTAMOGETONACEAE 



[CH. 



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

 crispus, L. (of. 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; w^ = conjunctive tissue (X130); 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 (x 290). [Schenck, H. (1886).] 



