STUDIES OP BRITISH FRESHWATER ALG^. 
51 
convenient substratum. Vaiicheria, when present, is often abundantly 
covered with Cocconeis Pediculus and some Coleoch(^te scutata, but 
the other epiphytes do not appear to occur on it ; this may, however, 
be due to the fact that they are not very abundant at the times at 
which the Vaucheria was found. Melosira often bears occasional 
tufts of Synedra radians and Achnanthes, but the other forms do not 
occur on it, and there is never much epiphytic growth. The same may 
be said of Mtci'ospora, on which only Epithemia has been found. 
Spirogyra and Mougeotia were both quite free of epiphytes.^ 
6^.— SUMMARY AND GENERAL CONCLUSIONS. 
We may briefly summarise the previous considerations as follows : — 
(i) The algal flora of the Fish Pond, Abbot’s Leigh, is dominated by 
a successive association (formation ? ) of Cladophora^ Spirogyra and 
abundant Diatoms (both free-living and epiphytic), while the principal 
subsidiary forms are CEdogoniiim, Mougeotia^ and Cya^iophycece. 
The algal flora shows a well-marked periodicity. 
(ii) Four phases are distinguishable in a normal annual cycle (see 
Plate and p. 34), viz. : — 
(a) Winter-phase with an abundance of free Diatoms. 
(h) Spring-phase with dominant Spirogyra. 
(c) Summer-phase with dominant Cladophora^ and abundant 
epiphytes. 
(d) Autumn-phase, chiefly characterised by renewed activity 
after the inactive summer-period, often wdth a prominent 
development of Spirogyra^ CEdogonium, or some other 
form. 
(hi) The majority of the species of Spirogyra present in the pond 
are found in some quantity, both in the spring- and autumn-phase, 
but some only occur in the former. The spring-phase is their period 
of maximum abundance and also their period of zygospore-formation. 
In two out of the five years, owing to abnormal conditions, 
Spirogyra was practically unrepresented during the spring-phase. 
A consideration of these abnormal conditions leads one to the view 
that the otherwise normally recurring Spirogyra-^ 2 ,%Q in the spring 
may be due to gradual concentration of the water, increased intensity 
of light, and the realization of a certain temperature. The autumn 
phase is then probably dependent on the simultaneous occurrence of 
the same conditions, and according as they are developed it is well 
or badly represented. The vernal reproductive process is considered 
to be due to a general intensification of the factors, liable to change in 
spring. This view finds support in the meteorological conditions 
preceding an abnormal case of zygospore-formation on the part of 
S. affinis in the autumn of 1907. 
^cf. Coraere, loc. cit., pp. 398, 399. 
