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POTAMOGETON TRICHOIDES Cham, in CAMBBIDGE SHIRE. 

 By Alfred Fryer. 



This species grows in the parish of Mepal, District 7 of Babing- 

 ton's Flora of Cambridgeshire ; it occurs iu one of the old natural 

 effluents of the now dried-up "West-Water," a former branch of 

 the River Ouse. With the exception of a single plant, the species 

 seems confined to a space of about a hundred yards on each side of 

 the bridge which carries "Ireton's Way" across that part of the 

 Sutton and Mepal Drain called "The Old Eau." I am thus exact 

 in giving the precise locality of the plant because I think this 

 peculiar distribution indicates that it is an old inhabitant of our 

 district, and not recently brought to us by water let in from the 

 rivers which run to Lynn, its West Norfolk station. 



When there is a deficiency of water in the summer, a small 

 sluice by the side of the old Bedford River near Welches Dam lets 

 in a sufficient supply, and as occasionally the old Bedford itself is 

 nearly dry, the tidal water from the New Bedford River is let into 

 it, in turn, and so we get the products of the lower waters brought 

 up to the fens thirty miles inland. 



I have long expected for this reason to find P. trichoides in the 

 ditches by the rivers or drains at Welches Dam, and have repeatedly 

 looked for it as far in that direction as Welney, in West Norfolk, 

 but hitherto without success. 



To return to the Old Eau : — Although I plumed myself not a 

 little on having found a rare species in a district where I had 

 predicted its occurrence as theoretically probable, I thought it 

 necessary to test the theory by carefully searching the drain from 

 Ireton's Way to the Sutton and Mepal Engine, where the water 

 when let in from the Old Bedford River first joins the main drain, 

 and thence runs up to the Old Eau. To my surprise, no trace of 

 the species occurred for half a mile, or more, and then a single 

 plant only was found ; beyond this plant I could not find a trace of 

 the species ; so it seemed as if this single plant had been brought 

 down from the Old Eau, rather than had ascended the drain to its 

 present station in that water. 



It is not improbable that when the tidal waters flowed up these 

 old natural streams, such as the old crooked Eau was at one time, 

 P. trichoides was more abundantly and widely distributed in the 

 fens. Evidently it now lacks some favourable condition necessary 

 to its growth, for its innumerable winter-buds are so freely produced 

 that a single plant might stock miles of river or drain in a single 

 season. It seems quite able to contend successfully with its fellow- 

 denizens of the drains ; as it grows freely amongst the densest 

 masses of Potamogeton, it evidently is not crowded out, as it prefers 

 to grow where vegetation is thickest. Unsuitable soil, moreover, 

 can hardly be the reason for its restriction, because the greater part 

 of the fens between Mepal and its West Norfolk station are on the 

 "silt," an ancient estuary deposit on which it grows near Lynn. 

 Possibly there is something in the nature of the water which does 



