200 LAND PLANTS IN WATER [ch. 



Cnicus pratensis^ it is interesting to note that a somewhat diffe- 

 rent water form has been described in the case of C. arvensis^. 

 The plant in question had suffered nine months' inundation in 

 a fenland flood; when observed in November, at first sight "the 

 leaf-rosette appeared normal ; . . . but on lifting it, it was found 

 to be attached to the ground by about 2 or 3 feet of slender 

 leafless stem of very soft and flexible consistency exactly re- 

 sembling the Woodless stem of a true aquatic. During the flood 

 Cnicus arvensis had evidently floated at the end of this aquatic 

 stem, much in the manner of, say, a Potamogeton or Callitrichey 



The present writer has noticed Ranunculus repens^ growing 

 by the water-side and putting out long runners into the water; 

 these runners bore leaves that were either submerged or rose 

 approximately to the level of the surface. Hydrocotyle vulgaris'^ 

 is also not infrequently seen either more or less submerged or 

 with a number of floating leaves (Fig. 132). 



A considerable amount of work has been done on the 

 anatomical changes induced by growing terrestrial plants or 

 amphibious plants in water instead of air. 



Among terrestrial plants, Vicia sativa, when grown in water, 

 does not develop aquatic characters in its epidermis, but the 

 xylem suffers marked diminution. This enfeeblement of the 

 xylem is characteristic of various other land plants when grown 

 in water, and, in the case of Ricinus and Lupinus^ there is a 

 similar reduction in the thickening of the bast fibres^. Rubus 

 fruticosus^ when grown in water, showed no change in the micro- 

 scopic structure of its sub-aquatic leaves and stem, except that, 

 in both organs, the chlorophyll was developed nearer the sur- 

 face than in the normal condition in air, while the hairs on the 

 stem tended to be unicellular instead of multicellular*; in the 

 shoots of Salix, also, little anatomical change was induced by 

 submergence^. 



1 Compton, R. H. (1916). 



2 The existence of these forms was noted by Gliick, H. (191 1). On 

 Hydrocotyle see West, G. (1910). ^ Costantin, J. (1884). 



4 Lewakoffski, N. (18732). 5 Lewakoflfski, N. (1877). 



