STUDIES OF BRITISH FRESHWATER ALG^E. 
41 
show that Cladophora (if present at all) is at its minimum during the 
summer in all pieces of water which attain a high summer temperature 
and are not artificially ceratedd To understand the marked decrease 
of the Cladophora during the wdnter it is necessary to notice the 
relation between it and the epiphytes which it bears. 
The most important epiphytes borne by the Cladophora are Diatoms 
(CoGConeis Fediculus, Sy7iedra radians, Epithemia turgida (Ehrenb.), 
Kiitz., Achnanthes, kc.) and occasionally species of Chamoisiphon. We 
may first notice the relation between the Cladophora and Cocconeis. 
The latter shows its maximum development almost at the same time as 
the Cladophora, although the curve of the latter generally commences to 
rise before that of the former. Some Cocconeis is nearly always to be 
found on the Cladophora, but it is generally least prominent during 
midwinter. Very soon after the Cladophora commences to put out 
fresh branches the Cocconeis begins to spread, and as it were to colonise 
the new ground. During the summer-months there appears to be a 
kind of struggle for supremacy between the Cladophora and the 
Cocconeis, the former continually putting out fresh branches and the 
latter soon afterwards settling down on them. At first the Cladophora 
gains ground, but subsequently it comes to be quite overgrown by the 
Cocconeis, which is generally accompanied by other epiphytic forms 
(Achnanthes, Chamcesiphon, Epithemia, Gompho^iema, Synedra radians, 
kc.^) This dense covering of epiphytes must have a very deleterious 
effect on assimilation (and possibly also on other functions of the Clado- 
phorcc). As long as the Cladophora is still able to put out numerous fresh 
branches, which are not immediately taken possession of by the epiphytes, 
these young branches can probably do all the assimilation necessary for 
the existence of the overgrown portions, but when this formation of 
branches ceases the Cladophora comes to be badly situated, and whole 
portions of it die away. This is, in our opinion, the explanation for 
the relative scarcity of Cladophora in the Fish Pond during the winter- 
months. Cladophora and the epiphytic forms just considered constitute 
something in the nature of a competitive association.^ 
Certain other of the epiphytes found on the Cladophora^, however, 
have a somewhat different relation to their host. This is notably the 
case with Synedra radians, which as a rule occupies the Cladophora 
during the winter-months {i.e. at the time of greatest scarcity of the 
latter) and is generally not very prominently developed in the summer ; 
it probably completes the damage done by the Cocco^ieis. This matter 
will be further considered below (see p. 42). 
As a consultation of the table (p. 37) and chart I. will show, 
Cladophora presents far more regularity in its annual cycle than does 
Spirogyra, and abnormalities, such as those shown by the latter in 1904 
^ cf. Fritsch, New Pliytologist, Vol. v. (1906), p. 153; also Proc. Roy. Soc. B., 
vo'l. Ixxix. (1907), p. 230, and Annals of Botany, Vol. xxi. (1907), p. 248, et seq. 
- cf. Comere, loc. cit. , p. 398. 
^Fritsch, loc. cit., pp. 161, 162. 
