BINARY FISSION AND SURFACE TENSION IN THE 
DEVELOPMENT OF THE COLONY IN VOLVOX 
Ro A. “HARPER 
Columbia University 
In Volvox we have an incipient metaphyte with a many-celled body 
of definitely organized form and the fundamental differentiation of 
soma and germ cells fully established. Klein’s (’89, ’90) argument 
that Volvox differs from true metaphytes in that the differentiation 
of the germ cells does not take place until after cell division is com- 
pleted is not very illuminating. The germ cells do not appear in 
Oedogonium until a considerable series of undifferentiated cells have 
been formed. Falkenberg’s comparison of the entire colony to a 
zoosporangium also overlooks the very important fact that in the 
development of the Volvox colony growth regularly alternates with 
cell division (at least after the first few divisions) just as it does in 
the development of the soma of one of the higher metaphytes. Vol- 
vox is frequently referred to as one of the best known algae. There is 
general agreement as to the order of cell divisions in the formation of 
the colonies, both for the egg and the asexual germ cells. The litera- 
ture has been frequently summarized. 
To proceed further with the study of Volvox from the standpoint 
of evolution and morphogenesis, we may compare it with such a 
simple coenobe as Gonium. In addition to their more obvious struc- 
tural characteristics there are two essential differences between the 
colonies in such forms as Gonium and Volvox. First, the adhesion 
between the daughter cells is much more firm in the latter. In 
Gonium, as all observers testify, the adult colonies break up into their 
component cells with the greatest readiness. I have figured such 
broken-up colonies (’12, Pl. V, Fig. 23). Slight pressure, change in 
the chemical composition of the medium in which they are, etc., lead 
to almost explosive separations. One marked difficulty in getting 
good photographs of the colonies is due to their tendency to go to 
pieces. On the other hand, Volvox shows almost no tendency to 
separate into its component cells. The colonies may be crushed into 
formless masses without isolating a single cell and I know of no chemi- 
cal or other stimulus which will cause their cells to fly apart as do 
those of Gonium. 
154 
