32 
STUDIES OF BRITISH FRESHWATER ALG^. 
play a great part, frequently (in the height of the summer) forming 
almost a complete covering on the surface of the water. Most im- 
portant of these aquatics are Potamogeton natans and P. crispus — 
especially the former — and Lemna minor, which forms dense patches, 
particularly around the edge of the pond ; Gallitriche is frequently 
present, but not in large quantity, while submerged mosses are not 
at all uncommon. Nasturtium officinale, Lythrum Salicaria, and 
Veronica heccabunga, are the chief representatives of the marginal 
vegetation. During the winter months Phanerogamic aquatics are 
often completely wanting or merely represented by a few plants of 
Lemna. 
The following ,is a list of the 
been found in the pond : — 
1. Cladopliora fracta, Kiitz. 
2. Spirogyra (Hass. ), Petit. 
3. ,, (Dillw.), Kiitz. 
4. ,, longata {Yn.\xc\\.),VJditz. 
5. ,, (Hass.), Kiitz. 
6. ,, nitida (Dillw.), Link. 
7. ,, rivularis, Rabh, ? ^ 
8. ,, wwiGTis (Hass.), Kiitz. 
9. ,, Webei'i, Kiitz. 
dominant species of Algae that have 
10. Melosira varians, Ag. 
11. Cocconema lanceolatum, 
Ehrenb. 
12. Fragilaria virescens, Ralfs. 
13. Gocconeis Pediculus, Ehrenb. 
14. Synedra radians, Sm. 
15. ,, Ulna (Nitzsch), 
Ehrenb. 
Although present in very varying amount at different times of the 
year the species above enumerated are the character-forms of the 
algal vegetation of the Fish Pond. Such a grouping of Gladophora 
with Spirogyra and an abundance of free and epiphytic Diatoms we 
have observed also in other pieces of water, and it is not improbable 
that it marks a definite type of freshwater algal formation (or associa- 
tion). Side by side with the character-forms several of the following 
species are generally to be found : — 
1. Mougeotia spec. 
2. GEdogonium spec, (varying 
from 5-40 g in thickness). 
3. Microspora spec. 
4. Goleochcete scutata, Breb. 
5. Glosterium moniliferum 
(Bory), Ehrenb. 
6. Oscillaria spec. 
7. Epithemia turgida(V\\Y&nb.), 
Kiitz., and other species. 
8. Navicula viridis, Kiitz., and 
other species. 
9. Gomphonema acuminatum, 
Ehrenb. 
10. Rhoicosphenia curvata 
(Kiitz.), Grun. 
11. Gocconema prostroium 
(Berk.), West. 
12. ,, cymbiforrne, 
Ehrenb. 
13. Achnanthes spec. 
Some of these subsidiary forms may occasionally become dominant 
(e.g., GEdogonium, Mougeotia), but this is an exceptional condition 
1 Diam. of filaments = 24-33 p ; three spirals. 
