106 BOTANICAL GAZETTE [FEBRUARY 
THE CCENOBIUM. 
The colony of U. Americana presents a somewhat similar 
appearance to that of Volvox globator L. That is, it consists of a 
more or less spherical sac of transparent jelly, in the periphery 
of which are numerous green cells provided with cilia which 
cause the organism to rotate slowly through the water. There 
the resemblance ceases, and in no way can the two be said to 
have a generic relation. 
In size and shape the Uroglena ccenobium varies greatly. 
While the general outline may be spherical, it is frequently found 
with protuberances and irregularities. All stages, from that of 
a perfect globe to a long cylinder with closed ends, have been 
observed, and many modifications of these extreme forms are 
apt to occur. The size varies as much as the shape. From the 
first early stages, consisting of but a few cells and measuring 
30—40p in diameter, we may have all gradations up to the some- 
what unusual size of 525 containing hundreds of individual 
cells. In the latter case the colony had been kept for some time 
under most favorable conditions, and probably represents the 
maximum growth. 
The individual cells are irregularly placed, and from 10-Z0p 
apart. There are no connecting canals as in Volvox. In regard 
to the structure of the interior of the colony of the original spe- 
cies (U. volvor Ehren.) there has been quite a difference of 
opinion. Ehrenberg (6) held that the contents were fluid, and the 
individual celis were drawn out into “tails,” all these ‘‘tails’’ 
being united at a common point in the center of the ccenobium. 
Neither Stein nor Biitschli observed anything of this kind, and 
considered it very improbable, Stein even maintaining that the 
colony was a homogeneous mass of jelly from center to circum- 
ference. Kent (5) confirmed the observations of Ehrenberg in 
regard to the appendage of the individual cells, and suggested 
that they might be contractile. Zacharias (7), in a recent article, _ 
brings forward the view that Us roglena volvox does possess an — 
internal network of threads or “tubes,” but he further maintains - 
iS that ‘the eee from each individual cell is not in 1 direct 
