CLEAVAGE IN DIDYMIUM MELANOSPERMUM (PERS.) MACBR. I3I 
ception is confirmed there can be no question that, in the best known 
forms of algal and fungous sporanges in which a multinucleated spore- 
plasm is cut up into one or relatively few nucleated spores, there is no 
trace of anything like the cell plate formed in the central spindle of 
the higher plants. 
It is evident that there is as yet no final agreement as to the types 
of cell division characteristic of the different families of plants nor 
as to the substantial uniformity of the process even within such a 
genus as Synchytrium or such a family as that of the Mucorineae. 
Much more careful descriptive work is needed before the limits of 
variation and the features common to all types of cell division can be 
determined. The slime moulds are certainly favorable material for 
such studies and the comparison of cell division in spore sacs which 
are so similar in externals as are those of Didymium and the Muco- 
rineae gives an excellent opportunity for determining the essential 
physical and mechanical features of the process independent of 
resemblances due to close relationship. 
The cleavage process has not so far been described for any of the 
Myxomycetes with simple spore sacs. The sporange of Didymium with 
its dome-shaped spore mass, large columella cavity and characteristic 
columnar stalk imitates a mucor closely though the method of its for- 
mation is quite different and the parts cannot be considered as homo- 
logous. It is questionable whether the term sporange should be used for 
such diverse types. De Bary (9) introduced the usage substituting the 
term sporange for the still more objectionable term peridium as used 
by the older authors on the assumed resemblances of Myxomycetes 
and Gasteromycetes. It is, however, hardly worth while in the present 
state of our knowledge to attempt to give any definite morphological 
significance to such a term used as it is indiscriminately for organs of 
ferns, algae and fungi without regard to phylogenetic connections. 
While the general shape of the dividing mass is strikingly similar 
in the sporanges of Didymium and the black moulds, in Didymium 
the spore-plasm at the time of cleavage is already pierced radially at 
regular intervals by the threads of the capillitium, while in the moulds 
it is practically a homogeneous mass. It is possible also in Didymium 
to obtain a view of the whole section of the dividing mass in a fashion 
not possible in the case of Fuligo and thus to study the mechanical 
changes in such a multinucleated cell regarded as a unit. 
I have photographed the principal stages for the purpose of bringing. 
