74 
E. Marion Delf. 
and in summer almost entirely replaced, by Vaucheria. On the 
cascades fruiting specimens have been obtained in the months of 
February, 1912, and in July and December, 1913. In the ponds 
V. sessilis has been found, both in February, 1912 and in December, 
1913, but it is much less common than on the cascades. There is 
thus no evidence for periodic activity in this form, which appears 
suddenly, persists for a lodger or shorter time, and disappears 
abruptly: on the whole, however, it prefers the colder months. 
The Akont.® (Conjugate). 
The Conjugate are perhaps the most characteristic of all the 
green algae of the ponds, appearing in great quantity from March 
to June, and in considerable amount in the late autumn months 
also. Mougeotia is the dominant form in ponds I and II, and has 
occasionally been locally abundant in V; various species of Spirogyra 
are also abundant, especially in ponds III, IV, V and VII. Desmids 
are never abundant, but Closterium has been found in every pond 
as an occasional constituent; Staurastrum has sometimes, and 
Penium very rarely, been seen. The occurrence of these genera 
will be considered separately. 
Several species of Spirogyra are present in the ponds, but only 
two have been observed to conjugate in nature; 5. decimina and 
S. bellis. Both of these have been found in great quantity, forming 
large sheets of submerged green on the bottom of the pond, as in 
III (November and December, 1913), or floating in tangled masses 
over the surface of the water as in March to June, 1912. Two 
other species of Spirogyra have been observed, 5. gracilis and S. 
nitida, the latter having once been seen to conjugate in a culture 
solution in the laboratory. These two species occur frequently 
but never in any abundance. There is a certain amount of constancy 
in the distribution of these four species. S. decimina and 5. nitida 
are characteristic of ponds II and III, and 5. decimina has also once 
been found in pond VIII (October, 1913). S. bellis, on the other 
hand, is constantly found in another part of pond III, and in ponds 
V and VII; the species do not seem to intermingle but occur in 
patches, side by side. 
The vegetative period of all the species fell mainly in March, 
April and May in 1912, followed by the fruiting period in June and 
early July. The first signs of conjugation were observed in the 
last week of May (ponds III, IV, V and VII), when the green 
slippery masses floating on the surface began to appear tangled 
