428 Frit sch and Rich . — Studies on the Occurrence and 
The ordinary curve of frequency of Spirogyra would thus either be 
a single one (with vernal phase only) or a double one (with both vernal and 
autumnal phase) with two maxima, one of which (in spring) would be 
much higher than the other (in autumn). Spirogyras are, however, occa- 
sionally found flourishing at other times of the year, and we must now 
notice a few cases of this kind. In the aquatics’ tank near the Jodrell 
Laboratory at Kew, vS. crassa is present in quantity practically all the year 
round, although it has not been found reproducing ; .S'. condensata and 
*S\ longata , however, are ordinarily only common in the same piece of 
water from June to August. This tank belongs to Comere’s 4 milieux 
mixtes,’ and the period of occurrence of the two Spirogyras last-named 
roughly agrees with Comere’s observations on such pieces of water (loc. cit., 
p. 405). 1 In a pond at Telscombe, near Newhaven, 5 . insignis (Hass.), 
Kiitz., was present in very large amount (but did not reproduce), in 
December, 1902, and January, 1903, although it disappeared totally after 
that, and did not occur again in the following winter. 2 affinis (Hass.), 
Petit, and S.cataeiiiformis (Hass.), Kiitz., were very abundant from September 
to December, 1904, in the same pond (cf. table). S', communis (Hass.), 
Kiitz., is frequently very abundant in midwinter in one of the ponds on 
Sheen Common, Richmond. We cannot do more than merely mention 
these cases, which no doubt any one of our readers could multiply. 
Further observation and experiment will no doubt bring an adequate 
explanation of these apparently abnormal phenomena. 
It still remains to consider a few examples of the reverse state of affairs, 
i. e. absence of a species of Spirogyra at a time when one would expect it 
to be present. One of the most striking cases of this kind is the complete 
absence of all species of Spirogyra in the first half of 1904 3 in Abbot’s 
Pool, although in 1905, 1906, and 1907 they were present in great amount. 
We are indebted to Dr. H. R. Mill for data as to the rainfall in the early 
part of 1904 and in the latter half of 1903. In October, 1903, the rainfall 
at Clifton was very much in excess of the average (=4*01 in. for the 
last thirty years), viz. 8-03 in. ; December also had a high rainfall, viz. 
3-13 in. The total rainfall from September to December, 1903, amounted 
to 16-4 in., as against 7-35 in. in 1904, 7-51 in. in 1905, and 11*13 in. in 1906. 
With reference to the sunshine, Dr. Mill writes : ‘ I cannot speak positively 
about the sunshine, as I have no statistics of it, but I think you may safely 
take it that the last three months of 1903, and the earlier months of 1904, 
were decidedly deficient in sunshine.’ There is thus good evidence to show 
1 Cf. Fritsch, Algological Notes. IV. Remarks on the Periodical Development of the Algae in 
the artificial waters at Kew. Annals of Botany, vol. xvii, 1903, p. 277; cf. also occurrence of 
Spirogyra in the lake at Kew. 
2 Fritsch, Problems in Aquatic Biology, &c., loc. cit., pp. 164, 165. 
3 Unfortunately, we have no samples from this pond before January, 1904, so that we are 
unable to say how long previously this state of affairs had obtained. 
