Reproduction of British Freshwater Algae in Nature . 429 
that prior to the abnormal absence of Spirogyra in Abbot’s Pool in the 
spring of 1904 the state of the weather was not at all normal (very excessive 
rainfall and lack of sunshine). That these conditions have something to 
do with the vernal appearance of Spirogyra is also exemplified by the 
remarkably late appearance of this genus in Abbot’s Pool (and other ponds) 
in the spring of this year (1907). Ordinarily, Spirogyra is quite abundant 
already in March ; this year, however, it did not occur in any amount 
before April (cf. the table). 1 As above shown, the rainfall in the autumn of 
1906, although not as great as in 1903, was considerably above that of 1904 
and 1905 ; this may again have something to do with the late appearance 
of Spirogyra this spring. There has, however, been a general dearth of 
Spirogyra 2 this spring, and we should not like it to be imagined that we 
consider the rainfall of the previous autumn solely responsible. The last 
year had a very long and hot summer, during which many of the smaller 
pieces of water dried up, and we have already pointed out that the ordinary 
water-level was probably regained too late for the proper development of 
an autumnal phase in any Spirogyra ; this may have acted as a check on 
these forms, which may be connected with their late appearance this spring. 
The spring of this year has moreover also been abnormal, and may be 
partly accountable. 
C. The Reproduction of Spirogyra in Nature. 
The fact that in most cases the species of Spirogyra reproduce during 
the vernal phase is a very marked feature in the biology of the genus (cf. the 
table on p. 436). The conditions which lead to reproduction at this time of 
the year must be very complicated ones, and we may quote the following 
examples in illustration of this. In the case of Abbot’s Pool, near Bristol, 
S', varians (Hass.), Kutz., has been found reproducing abundantly in the 
spring of 1905, 1906, and 1907 ; S. Weberi , Kutz., and S', affinis (Hass.), 
Petit, although present in all three years, formed zygospores only in 1906 ; 
S. nitida (Dillw.), Link, was present both in 1905 and 1906, but reproduced 
only in 1905; while S. neglecta (Hass.), Kutz., formed zygospores in both 
years. In all three years S', varians was found with zygospores in two 
other ponds during the vernal phase (cf. the table). In the case of this 
species, therefore, the conditions necessary for reproduction appear to be 
realized every spring ; while in the case of the other species mentioned 
above, the factors which lead to conjugation only occasionally obtain. 
Similar observations were made on the Spirogyras in Barton’s Pond, near 
Harpenden ; S. tenuissima (Hass.), Kutz., was reproductive in both 1906 
1 Reproduction also set in considerably later than usual. 
2 In some ponds, which ordinarily have a good deal of Spirogyra in spring, it has scarcely put 
in an appearance up to the time of writing (June 3), e. g. Hendon Pond. 
