52 
STUDIES OF BRITISH FRESHWATER ALG.E. 
(iv) The genus Cladophora is to be found in the Fish Pond all 
the year round, although in varying quantity. It reaches its maxi- 
mum in the summer and its minimum in January and February. 
The small amount present in the winter is considered to be due to 
the deleterious influence of the rich growth of epiphytes found on 
the Cladophora in the latter half of the summer and in the autumn, 
while the relative abundance of this Alga in the warmer months is 
ascribed to the fairly low average temperature of the water. 
(v) Diatomacese are very important constituents of the algal flora. 
We may distinguish two phases : One in which the free-living forms 
(Meloszra, Fragilaria^ Coccoziezna, also the epiphytic Synedra 
radiazis) dominate, and the other in which the epiphytes ( Coccozieis^ 
Epitheinia ) dominate. These two phases are the winter- and summer- 
phase respectively. Cladophora with its epiphytes ( Synedra radiazis^ 
Cocconeis, Epitheznia ) constitutes a competitive association. 
(vi) The reproductive processes in the pond show considerable uni- 
formity, which is ascribed to the rather narrow range of temperature 
of the water. Resting-stages have only been observed in four forms 
( Spirogyra^ Meloslra, Vaucheria^ and Cladophora all the other 
species (e.g. of Mougeotla, (Edogoniimi^ Microspora^ etc.) appar- 
ently regenerating by vegetative or asexual reproduction of a few 
persisting individuals. In the case of Spirogyra^ Meloszra, and 
Vazicheria the formation of resting-stages immediately precedes a 
period of very diminished occurrence of the form in question, while in 
the case of Cladophora dormant filaments are the winter-condition. 
Asexual and vegetative reproduction (in (Edogozzmvz, Mozigeotia, etc.), 
naturally precedes and coincides with an increase in amount of the 
form concerned. Auxospore-formation in Meloszra often coincides 
roughly with the end of the winter-phase, zygospore-formation in 
Spirogyra with the end of the vernal phase, while the assumption 
of the winter-condition on the part of the Cladophora indicates the 
approaching end of the autumn-phase ; the commencement of the 
autumn phase is marked by extensive vegetative and asexual repro- 
duction (in Spirogyra, CEdogoniuzn , etc.). 
(vii) The epiphytic algal vegetation, which is so richly developed 
in the pond, finds its chief host in Cladophora (also the Phanero- 
gamic aquatics). CEdogozzizinz comes second, but only bears forms 
attached by a narrow base {z.e. it lacks Cocconeis and Epitheznia), 
while Coccozieis is the most abundant epiphyte on the broad filaments 
of Vazicheria. The Conjugates bear no epiphytes. 
(viii) The entire algal vegetation was most strikingly developed 
in the year 1905, which was characterised by uniformity of tempera- 
ture and abnormally low rainfall. 
One of the most salient features in the annual cycle is the struggle 
between Cladophora and its epiphytes ; these constitute one group of 
forms, apparently little influenced in their development by any others. 
