44 
STUDIES OF BRITISH FRESHWATER ALGiE. 
eously with the increase of Cladophora, and remains a dominant form 
up to the late autumn. The same is true to a lesser extent of Epithemia 
and Achnanthes. These genera, therefore, do not seem to be so 
susceptible to summer temperatures as the forms previously discussed. 
There do not appear to be any obvious climatic factors that would 
account for the scarcity of these forms during winter and early spring, 
and it seems more probable that their relative scarcity during these 
latter periods is due to their killing a large portion of their sub- 
stratum {Cladophoraj cf. above) and to the dying away of other parts 
of it (namely the Phanerogamic water-plants). Very probably also 
Synedra radians^ which seems to flourish best in the colder months, 
and during that period occupies a good deal of the surface of the 
Cladophora {cf. above), crowds out the Gocconeis to a considerable 
extent. There would thus be competition between the Cocconeis and 
the Synedra for the occupation of the surface of the Cladophora^ which 
is itself endeavouring to escape from its epiphytes. 
(iv.) — (Edogonium. 
The genus (Edogonium^ although rarely a dominant feature of the 
vegetation of the Pish Pond, is almost invariably to be found inter- 
mingled with the other forms, and may therefore be briefly considered. 
It is apparently represented by a considerable number of different 
species, but as none of them have reproduced sexually during the 
period of observation, it has not been possible to determine them. 
The diameters of the filaments vary between 6 p and 41 /x, and 
between these limits filaments of practically every width are found. 
It does not appear that any particular width of filament is especially 
prominent at any definite time of the year. 
The species of the genus in question are generally rather more 
abundant in the colder months of the year (November to February 
or March) and are always least conspicuous during the spring months, 
the latter phenomenon being possibly due to the crowding out 
influence of the then dominant Spirogyra. We have, however, not yet 
undertaken a sufficiently detailed study of the genus (Edogonium to 
be able to say anything as to its normal annual cycle, and must 
leave that to a later communication. The only time at which 
(Edogoninm played a really prominent part in the algal flora of the 
Fish Pond was during the last six months of 1905. Already in July 
and August of that year it was an important form, i.e. at a time 
when it is usually quite at a minimum. We are unable to ofiPer any 
explanation for this, but it may be noticed that 1905 altogether 
showed an exceptionally rich development of the algal flora in the 
pond we are discussing (cf p. 34). 
( V. ) — CyanopliycecE. 
The Cyanophycese are, on the whole, very subordinate constituents of 
the algal flora of the Fish Pond, but as they show one or two points 
of interest, they may just be briefly touched upon. At most times of 
the year blue-green alg« are present only in very small numbers, and 
