VASCULAR SYSTEM OF AQUATICS 



173 



phyllum. It may be noted that the leaf-traces exhibit a similar 

 reduction, one bundle passing to each leaf in the last-named 

 species, whilst in the two former the trace consists of three 



FIG. 90. Portion of transverse section of the stem of the Mare's-tail 

 (Hippuris). Co., lacunar cortex ; En., endodermis ; p. phloem ; 

 pi., pith ; Xy., xylem. 



bundles. In view of the reduction which water-plants show in 

 respect to the vascular tissue, it is scarcely surprising that they 

 rarely exhibit cambial activity. A trace of cambium can, how- 

 ever be detected in the stem of the Mare's-tail (Hippuris). 



