4 
THE JOUltNAL OF BOTANY 
The common deep-water form (No. 7, Table I.) has been named 
var. lanceolatus Blytt ( = var. gracilis Chamisso). It possesses long, 
nearly parallel-sided, but slightly tapering leaves of extremely thin 
texture and light green in colour. It occurs in many of the lakes, 
but is most abundant in Coniston, where its extreme form (No. 8) 
has been wrongly identified as P. Ricliarclsonii —a species not yet 
met with in this country. 
A form (No. 5) possessing very large and broad leaves of darker 
colour and thicker texture than usual with us, has been termed 
var. macrophyllus Blytt. This is found only in Ullswater. 
The common form of relatively shallow waters and high light- 
intensity (No. 2), possesses small oval-oblong leaves, and is frequently 
met with in Windermere, Esthwaite, Derwent water, Ullswater, and 
Hawes Water (69«). Hodgson (FI. Cumb. 316) gives it also for 
Bassenthwaite and Crummock, but we have not yet seen it in either 
lake. 
In Potamogetons of the British Isles (p. 40) the peduncles of 
this species are stated to be from 2" to 2j" in length. We have 
them long from Windermere. 
P. pilelongus Wulfen is a characteristic and beautiful deep¬ 
water species frequently occurring in the lake-waters up to 9 m. in 
depth, but uncommonly in water of less than 2 m. in depth. The 
variation in leaf-form apparently follows that of P. perfoliatus but is 
much less extreme. The following table (HI.) summarises the 
variations observed and their relation to the environmental con¬ 
ditions :— 
Average leaf. 
Length 
Soil. 
K,0 
Length. Breadth. 
breadth. 
K,0. 
CaO. 
CaCL 
Windermere. 
Normal form 
Deej) water, 6 
. 15 
mm. 18 
2-5 
2-7 
6-0 
6-7 
420 
1260 
0-33 
Ullswater 
(Average) . 
. 16 
2-4 
6-7 
340 
280 
1-2 
Esthwaite (a) 
. 16 
3*0 
5-3 
(&) 
... 
. 10 
2-3 
4 3 
460 
2400 
0-2 
Lengths and breadths are averages of 10 mature leaves. 
The Esthwaite forms are strikingly different from any others we 
have seen, the leaves being much broader in proportion to their 
length. During 1919, when considering the ecological changes 
taking place in this lake, we ventured to anticipate the probable 
early appearance of this species, and discovered it there for the first 
time in August 1920. P. prcelongus also occurs in Windermere 
Coniston, Ullswater, and Derwent water. 
P. lucens is a deep-water species very locally found in Winder- 
mere, Coniston, and Hawes Water, Silverdale (v.-c. 60). This species 
does not occur in Derwentwater, the record of it by C. Bailey for 
“ N.W. end of Derwentwater” (FI. Cumb. 315) referred to P. Zizii 
which still grows there in abundance. 
It shows little or no variation in form in this area, but the leaves 
of the plants growing in the calcareous Hawes Water are always 
thickly encrusted with carbonate of lime. This tarn, however is 
outside the limits of the Lake District proper, and should not be 
confused with the lake of the same name in Westmoreland. 
