Wicken Fen. 
69 
of the Fen. But in reality one finds on Wicken Fen all kinds of 
plants intermediate between on the one hand, those that live sub¬ 
merged in water, and on the other hand, mere aliens which have 
migrated from the surrounding dry lands to the drier parts of the 
Fen soil. The following list (the result of many observations in 
the Fen district and elsewhere) is an attempt to place some of the 
commoner marsh plants approximately in order, with respect to the 
degree of soil moisture which would seem to be the optimum. It 
must be remembered however, that such a list can be at best only 
a tentative one, as each species will possess a wider or narrower 
range of possibilities as to the moisture conditions to which it can 
adapt itself. For instance, Hydrocotyle vulgaris and Polygonum 
amphibium possess a very wide moisture range, while many sub¬ 
merged aquatics, e.g., Potamogeton lucens, have but a narrow one. 
Further, this list refers to the conditions in respect to soil moisture 
only. The effect, scarcely less important, of varying atmospheric 
moisture will be dealt with in a future paper. 
The list 1 then represents the average relative positions, with 
respect to soil moisture, in which, so far as my experience goes, it 
is most usual to find the subterranean parts (roots, rhizomes, &c.), 
of some of the characteristic Fen plants. 
A. Aquatics. 
1. — Char a, Nitella, &c.—whole plant submerged. 
2. — Myriophyllum, Potamogeton , Hottonia, &c.—vegetative 
parts submerged, flowering shoots above water. 2 
3. — Nymphaea, Sparganium natans, &c.—leaves floating. 
B. Semi-Aquatics. 
4. — Sagittaria, —submerged and aerial leaves. 
5. — Scirpus lacustris, —submerged leaves and tall green aerial 
stems. 
6. — Butomus umbellatus , Sparganium erectum, Alisma Plantago, 
( Polygonum amphibium )—aerial leaves. 
C. Wet-Marsh Plants. 
7. — Phragmites communis. 
8. — jf uncus obtusiflorus, Cladium Mariscus. 1 
9. —Many of the Carices, Orchis incarnata, Caltha palustris, 
Menyantlies trifoliata. 
1 The names used in this paper are those given in Britten and 
Rendle’s List of British Seed-plants and Ferns. London, 1907. 
2 Sometimes even the flowering shoots may be submerged, e.g., 
last May I found some specimens of Hottonia palustris 
submerged in rather deep water. Many of the flowers had 
fully opened under water, but were much smaller than the 
normal ones. 
