374 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
different algae on this point and that the kind of substance and the amount best 
suited to development must be determined for every alga selected for culture. 
While some grow more luxuriantly in a purely inorganic solution, others, among 
which are the unicellular blue-green algae, seem to prefer a solution where at most 
but a trace of mineral matter is present. The culture medium most favorable in a 
large number of cases was a decoction made from the organic matter of the plank- 
ton. This seemed especially favorable if large quantities of Anabce,na fios-aquce were 
present. This observation that the organic matter of the water could be used by the 
algse has suggested a possible explanation of the great increase of algse at certain 
seasons, causing the “water bloom.” This phenomenon has been observed by the 
writer but three times, but at each time it was known that an unusual amount of 
dead organic matter was in the water of that vicinity. At one time the matter was 
in the form of numerous small dead fish floating on the water; at another time a 
quantity of refuse had been emptied into the bay where the water bloom was noticed; 
and a third time large areas of the surface of the water were covered with the skins 
of Ephemera which are shed before the insect reaches the imago state. Such phe- 
nomena as these can be explained only experimentally, and it is along these lines of 
increase and source of nutrition that further investigation should be carried. 
THE STRUCTURE AND LIFE HISTORY OF CERTAIN PLANKTON ALGjE. 
Chlamydomonas gracilis Snow, new species. 
This species of Chlamydomonas (fig. i) in its most vigorous and normal motile condition is 
cylindrical, ovoid or ellipsoidal in shape, rounded at. the posterior end and bluntly pointed at the 
anterior end. Length 10.5 to 13 //; breadth 5 to 6.5 y. In the nonmotile condition the cells are 
ovoid or spherical, and often motile individuals of the same shape are noticed, with a diameter of 9 
to 10.5 y. The chloroplast and entire contents are sometimes withdrawn from the membrane either 
at the anterior or posterior end. When at the anterior end the two protoplasmic flagella can be seen 
to be continuous with the protoplasm within. The flagella are somewhat longer than the cell. 
The single hollow chloroplast lines the membrane throughout, except for a very small area 
just at the anterior end, at which point two pulsating vacuoles can be seen. The color is a dull 
bluish-green, rather than a vivid green. Oil is always present. The pyrenoid is in the extreme 
posterior end of the cell. The pigment spot is a conspicuous dull-red disk, and is often situated 
as far back as midway between the two ends or even farther. The nucleus occupies & position 
between the center and the anterior end of the cell. After division the cells are liberated by the 
enveloping membrane becoming dissolved at one point, through which the new individuals escape, 
leaving the empty membrane behind. 
Tliis species, like most species of Chlamydomonas, grew and reproduced readily in a 0.2 to 0.4 
per cent Knop's solution, and this culture medium was used to trace the life history of the species. 
On transferring material from Knop’s solution to water, individuals were formed which were 
taken to be the gametes, though only in one instance was indication of copulation noticed (fig. I, 4). 
These were in all respects like the ordinary motile form, except that they were smaller, ovoid in 
shape, and had no membrane (fig. i, 3) . Though the species resembled Chlamydomonas debaryana 
Goros., it is much smaller and more cylindrical in shape than that species. 
This species was found 21 miles north of Kelley Island, in Lake Erie. It is by no means widely 
distributed in the water of the lake. 
Chlamydomonas communis Snow, new species. 
This species in the motile stage resembles closely the preceding species, but after cultivating 
the two forms in pure cultures side by side for over two years, and finding characteristics which are 
distinguishing and constant, they have been separated into two species. The size and shape of the 
two are almost identical, the shape being oval or ellipsoidal and pointed at the anterior end (fig. ii). 
