150 HETEROPHYLLY [CH. 



Where the three types were borne together, the simply-pinnate 

 leaves were the latest to be produced, and the submerged leaves 

 the earliest, while the compound- 

 pinnate air leaves were intermediate. 

 Oenanthe Phellandrium, Lamk. 

 v&r.fluviatilis, Colem. 1 is very com- 

 mon in the Cam near Cambridge. 

 It has graceful, finely cut, pinnate 

 leaves with obcuneate segments, 

 and the plant is generally entirely 

 submerged; a shoot as long as 

 235 cms. has been recorded. Its 

 identity is liable to be puzzling at 

 first sight, since its aerial axes are 

 comparatively rarely to be found. 

 On one occasion, however, on 

 which the present writer found the 

 plant bearing both submerged and 

 aerial leaves, Oenanthe Phellan- 

 drium (proper) was noticed, at the 

 same time, growing magnificently 

 in a neighbouring ditch. It had 

 a very stout, lacunate stem, bearing 

 numerous aerial leaves and also a 

 relatively small number of sub- 

 merged leaves with capillary seg- 

 ments; the abundant lateral roots 

 were lacunate. A comparison of the 

 two plants suggested that Oenanthe 

 Phellandrium var. fluviatilis is a 

 mutation which has taken more 

 whole-heartedly to water life than 

 the type form of the species. 



Polygonum amphibium is an example of a hydrophyte which 



1 It is a matter of opinion whether this plant should be regarded as a 

 distinct species or as a variety. See Coleman, W. H. (1844). 



FIG. 98. Sium latifolium, L. Sub- 

 merged leaf from a plant found at 

 Wicken Fen, June 27, 1914. Less 

 finely divided than leaf a in 

 Fig. 97. (Reduced.) [A. A.] 



