139 
It was strange to find on grass-covered sand-flats near the 
ford over the Rio Grande great numbers of a flat dried-up Nostoc 
growth when it rains so much that the river rises and covers the 
flat at least part 
m an excursion on the xs1th of February to the sugar fields 
south of Mayagiiez, I found in the ditches which were ed 
or wholly filled with water a rather rich vegetation of Chlor 
phyceae, as Spirogyra (with habeas Pithophora, Stil 
the Uro 
nema-like alg: ich e has ace e 
greenhouses of Columbia University, but the original locality 
which was unknown. I have found this alga at several places 
in Porto Rico. 
Most interesting, however, was the stay at Maricao, which 
was one of the best localities for algae on Porto Rico. I col- 
fected algae there twice, viz., February 12-15 and 19-22, during 
which i 
with zygotes. On the contrary, both Zygnema and Spirogyra 
had a very frequent vegetative propagation by individual cells, 
which separated themselves from each other and as propagative 
akinetes gave origin to new fila pose that the 
conditions depend upon the fact that the conditions of life nearly 
year round are practically unchanged mpera- 
ture is rather constant and at ace where the unt of rain- 
e ri 
fall is so great and rather equally distributed throughout the 
year, there will scarcely arise times when the algae need resting 
stages in order to carry them over a period of drought. 
There also was found an unusual abundance of aerophilous 
algae in the vicinity of Maricao. Especially were the larger or 
smaller declivities of red clay very often colored green or 
