234 PROCEEDINGS COTTESWOLD CLUB 1914 



or held up among herbage, they often show Uttle embryo 

 roots or processes which, in contact with the ground, might 

 develop their true character. It is quite common for the 

 signs of rooting to extend to the end of the branch, though 

 apparently sometimes with omissions in the middle. But 

 sometimes these side stems, even if prostrate on bare ground, 

 show no evidence of the rooting character. Again, on different 

 flowering branches of one and the same plant, the rooting 

 character is strongly present and nearly absent, at the same 

 moment. At one time, I thought the rooting character a 

 means of diagnosing the suil rather than the variety of H. 

 nodiflonim, but that opinion now appears to me at variance 

 with actual facts. It seems impossible at present to explain 

 the variations of this feature. 



Other characters, e.g., length of peduncle and shape of 

 leaflet, are as untrustworthy as that of " rooting," for pur- 

 poses of critical diagnosis. The form taken by the species 

 is very largely determined by the surrounding vegetation, 

 and by the amount of water present. It is a common thing 

 to find the same series, or even the same plant, changing 

 suddenly from the small — or medium — leaved form, with its 

 compact foliage and low growth, as it runs among the open 

 grass by a tiny rill, to the large ditch form, with its tufts of 

 great upright leaves, and large coarse stems and branches : 

 the change being due only to the shade of a copse or bramble. 

 In 1913, early in the summer, I found a large, rather 

 coarse, form growing by the side of a pond near Llandaff : 

 it was vulgare F. Schultz. Later on, in August, the water 

 had receded considerably, and left a broad, soft, muddy margin. 

 The plants had been broken off quite short, but were shooting 

 again from the same roots ; this time the form produced was 

 small, compact, rooting at the joints, and, in fact, very close 

 to pseudo-yepens H. C. Watson. The circumstances had 

 changed in one vital respect, and the plant had consequently 

 changed entirely in appearance. 



Hence my third — though somewhat tentative — conclusion 

 follows. It is clear that some of the supposed varieties, at 

 any rate, are simply transient forms due to special circum- 

 stances, such as the amount of water present, the amount of 



