Our Fresh- Water Alge. 671 
organs, the alga often combines them all in a single cell or ultimate 
constituent. “In cases where the alga is composed of many cells 
the same principle often holds good, each cell being sufficient unto 
itself, uniting within its own small limits all the multifarious em- 
ployments or functions which make up the life-activity of its species, 
and therefore able to live equally well if by accident it becomes 
detached from its associated cells. Hard-working cells are these, 
for they have not yet learned the rudiments of the division of labor; 
cells of manifold activities certainly, and correspondingly hardy, 
self-dependent, and ever unsubdued. They live and replenish the 
earth unseen by man, till by effects or masses of individuals they 
move him to wonder, and, as in the middle ages, to ascribe their 
sudden-seeming presence to the wrath of heaven or the agencies of 
the black art or to the medium of alchemy. 
The present needs will not permit my entering into the subject 
of the scientific classification of the alge, but it may be of service to 
notice some of the principal groups for which common names are 
in use, According to habitat we may divide all alge into the 
marine and fresh-water divisions, including with the latter the 
erial species, surface-dwellers on moist earth, sand, rocks and trees. 
Recombining all the alge, they may be again divided according to 
coloring matter, contained, generally as a liquid, in their cells, 
classing them therefore as fhe red, olive and green alge, and 
fourthly as the Phycochroms, the last having as their characteristic 
a bluish cast seen in the green, ashen or grayish hue which pervades 
them. The red alge, so prized by collectors on the shore, are 
scantily represented in our inland waters ; the olive do not appear 
at all ; but the two other divisions find in fresh-water their chief 
representation. The green alge of the tide-marshes along the coast 
are very conspicuous, and of uncounted numbers, but of very few 
species comparatively ; those of fresh-water are probably still more 
abundant in individuals, certainly in species. The Phycochroms 
never reach as great a size as do members of each of the other 
sections ; they are, indeed, chiefly microscopic, as individuals, if not 
as Masses or colonies, Their cell-contents are also less highly 
organized. Their chief abode is in slowly running streams and 
quiet waters, They are the Cyanophyces of Goebel and of various 
authors since Nägeli, in 1849. They are remarkable for the pres- 
