376 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
passing into a resting condition the ends become more rounded and the shape more ellipsoidal. In 
the mature resting stage the cells are spherical (fig. Iv, 2). 
The membrane is perfectly smooth without processes or markings of any kind. The composi- 
tion of the membrane is cellulose, turning blue when treated with iodine and sulphuric acid. In 
the younger individuals the membrane is comparatively thin, but when the cell passes into a rest- 
ing condition the membrane becomes very much thickened, is 2.5 to 3.25 4 in diameter, and two, 
three, or sometimes four layers are distinguishable. The thick inner layers are also of cellulose, 
while the outermost layer becomes to a greater or less degree cutinized. As the cells pass into a 
resting stage and become spherical in shape, the surface of contact between two adjoining cells 
becomes less and less, and finally they break away from each other and exist singly. 
The chloroplast, under natural conditions, is a thin, homogeneous layer, irregularly interrupted 
at the center, and forming a lining to the membrane. At one side near this point a large pyrenoid 
is present. Under cultivation, in most media, the chloroplast assumes a granular appearance on 
the surface and the perforations are obscured. Later a large amount of oil is developed which is 
readily dissolved in absolute alcohol. As the cell passes into a resting condition this oil gradually 
assumes an orange color. On account of the ease with which the cells pass into a resting condition 
the normal condition of the chloroplast can with difficulty be maintained under cultivation. 
The nucleus is small and les near the pyrenoid, sometimes on one side, sometimes on the other. 
Staining with hematoxylin brings out the presence of several large vacuoles in the cell cavity. 
In its relations to external conditions this variety seems in many ways to deviate from most 
other alge. Ina numberof solutions, found generally to be favorable for algal culture, this variety 
simply passed into a resting condition. The only solution tried which really proved to be favorable 
was a solution of decaying Anabena flos-aque, which occurred at times in great quantities on the 
surface of the lake. In this the development seemed normal.~ In an organic solution (decaying 
peas) and in 0.2 per cent Knop’s solution the color became green and healthy, but no reproduction 
occurred, at least for many weeks. <A solution from the organic material of the plankton 
proved favorable to reproduction, but old and young coenobia alike soon became filled with orange- 
colored oil, passing into a resting condition, and remained in this condition until the nutrition of 
the medium was finally exhausted, or until they were transferred to.a fresh and favorable solution. 
Of the inorganic solutions, Sachs’s, Knop’s, Oelmann’s and Knop’s solution without calcium, . 
Sachs’s solution was the only one that was at all favorable. Here reproduction occurred readily, 
and the cells assumed a normal appearance, but even in this solution, after a time, the coenobia 
gradually passed into a resting condition. 
Staurogenia apiculata Lemm. 
This species, which is very generally, though not universally, found in the plankton of Lake 
Erie, is undoubtedly that described by Lemmerman 798 as Stawrogenia apiculata. His figure 
and measurements agree quite closely with those of the Lake Erie species, though his description 
leaves us in some doubt in regard to details. 
In Lake Erie this alga may occur either as individual coenobia, composed of 4 ces lying in 
one plane (fig. v, 4,5), or these coenobia may be united into large, more or less irregular rectangular 
plates of cells, measuring 50 to 150 ~ on a side (fig. v, 1). 
The 4 cells of the ccenobium are either lemon-shaped or oval, and are arranged to form a 
rectangle with a diamond-shaped space at the center. Of all the species of the Canobie, this 
is apparently the most constant in regard to the number of cells. In other members of this 
tribe the number of cells of any daughter individual depends very largely upon external conditions 
and the vitality of the parent ccenobium, but of the many thousand ccenobia of this species examined 
under widely varying conditions, only one individual showed any deviation as to number of cells. 
In this case division was incomplete and but 3 cells were formed instead of 4, though four pyrenoids 
were present. E 
The large plate-like structures which are found in the tow, and which also occur in cultures, 
arise from the daughter coenobia remaining after liberation in the position in which they are 
formed (fig. v, 1), being held in place by a colorless, gelatinous substance which surrounds each 
individual. As each of the 4 cells gives rise to a daughter ccenobium of 4 cells, all of which lie in 
the same plane, a plate of 16 cells is formed, and as each of these again produces a coenobium, 
a compound ccenobium of 64 cells is produced. This process continues, but the plate-like struc- 
