F. E. Fritsch. 
166 
more delicate species than the one which flourished in the pond 
at the same time in 1903. 1 Mr. Boodle had visited the pond 
earlier in the same month and informed me that there was then a 
considerable amount of 6'. gracilis in it. In the samples taken on 
Feb. 14th and March 20th, 1904, matters were much the same, the 
Oedogonium crispulum remaining sterile, whilst O. inversum, which 
occurred so abundantly in the winter of 1903, began to put in an 
appearance. In the next month (April 20th, 1904) I was much 
astonished to find that this latter Oedogonium had increased very 
largely in amount and bore numerous oogonia ; the Spirogyra gracilis 
became replaced by another species of the same genus with broad 
short cells (S. condensata). On May 15th, whilst Oedogonium 
inversum still occurred as the most prominent form and bore 
numerous oospores, Spirogyra condensata had also become a great 
feature of the algal vegetation: the latter Alga was in part vege¬ 
tative, in part however passing over to a condition of fructification 
exhibiting lateral conjugation. The fact that both the Oedogonium 
and Spirogyra were in a sexual condition led one to expect that 
these species were near the end of their development, and a glance 
at the next month’s sample (June 26th) shows that this was really 
the case ; Spirogyra condensata had then quite disappeared from 
that part of the pond which it occupied on May 15th, although a 
small patch of it was still present on one side. The next sample, 
collected on August 10th, showed no trace of the Spirogyra, 
although the Oedogonium persisted in small quantity.—During this 
whole period, as in the previous year, the other species of 
Oedogonium (O. crispulum , Wittr. & Nordst.) was observed in small 
amount; in the sample taken on September 18th, 1904, finally 
it was found to be rather commoner and to be proceeding to form 
oogonia; six weeks later however (October 30th) it had practically 
disappeared and was probably in the resting condition. The sample 
of September 18th showed another interesting feature, viz. the 
great development of Spirogyra gracilis (Hass.) Ktz., which together 
with the Oedogonium, formed the dominant algal form and like it 
showed indications of the commencement of the sexual process. 
However it managed to persist, and to become even commoner 
in the subsequent months and was still the most abundant form in 
the pond on December 26th; during the whole of this period 
1 The pond was covered bv a sheet of ice when this sample was 
taken, so that its collection was a difficult matter, and it is 
possible that there was really a larger amount of the fila¬ 
mentous species present than the sample indicated. 
