1900] Stone, — Luxuriant development of Spirogyra crassa 33 
extreme variation, however, is not allowed for in the descriptions and, 
were a group of such forms found in an isolated station, they might 
easily prove puzzling. Among the specimens submitted were two 
buttons nearly white at first, which, after lying a few hours in the dry 
air of a room, turned browner, a part of the surface cracking into 
scales. 
Such instances of variation occurring in common fungi show the 
necessity, so strongly emphasized by Fries, of keeping close and con- 
stant watch of plants in the field from year to year, and they further 
suggest the possibility that in the case of species of rare occurrence 
and solitary habit, such as, for instance, Amanita strobiliformis and its 
allies, it may be that forms have been kept separate which should really 
be closely associated. 
LUXURIANT DEVELOPMENT OF SPIROGYRA CRASSA 
IN REFILLED PONDS. 
G. B. STONE. 
Spirogyra crassa, Kuetz., one of the largest species of the genus, 
has been under my observation, more or less, in an incidental manner, 
for some twelve years. A peculiar trait which I have repeatedly 
observed, and to which I wish to call attention, is its remarkable abun- 
dance under certain conditions. In every instance the unusual abun- 
dance of this species was connected with the drawing off the water 
from artificial ponds, the drying up of the bed, and the subsequent 
refilling. I know of four instances where ponds have become dry, and 
in every case there has been a luxuriant growth the following season of 
this species, not common before in these ponds. 
In two cases the locality was the pond in the Public Garden in 
Boston, the first occurring in 1886, the second a few years later; the 
third case was that of a small pond at Spencer, Mass., in 1889 ; the 
fourth, a pond in the Agricultural College grounds at Amherst, Mass., 
in 1893. In all these instances the plant was so common that it 
almost completely covered the surface of the water, at Amherst it 
became a nuisance, and cartloads of the floating filaments were gath- 
ered and carried away. Similar results, to a less noticeable extent, 
have been observed under similar conditions in ponds in Worcester. 
The Spencer and Amherst ponds are contaminated with sewage 
