CLEAVAGE IN DIDYMIUM MELANOSPERMUM (PERS.) MACBR. I4I 
seen in the central spindle and polar asters and which play so im- 
portant a role in the phenomena of cell division and free cell formation 
in the higher plants and in the ascus. 
None of the mechanical theories of cell division like those of 
Heidenhain and Kostanecki, which also involve the existence of a 
special system of organic rays for each nuclear center, can have any 
application, as I have pointed out before, in cases of progressive 
cleavage of multinucleated masses such as we have in the spore sacks 
of the slime moulds and fungi. 
Swingle (29) has clearly diagrammed the tension relations involved 
in the cleavage processes of these sporanges, whether or not the 
furrowing is really due to localized contraction of the cytoplasm, as he 
supposes. The cleavage furrows whether originating from the vacu- 
oles, the periphery of the mass or the capillitial canals constitute a 
complex system of catenoidal surfaces which tend to divide the mass 
into spherical fragments. Such cleavage surfaces may equally well 
be conceived as due to exudation of water with increase of surface 
tension between the cytoplasm and the extruded moisture due to the 
ripening changes going on in the former, involving, as they probably 
do, condensation processes with change from highly hydrated proteids 
to lipoid or other fatty storage products. Such chemical changes 
may well play a part in the liberation of the energy necessary for the 
accomplishment of these profound form changes. 
I have elsewhere suggested (14, 16) that in the gradual shrinkage 
and condensation of the spore-plasm the loss of water might be least in 
the neighborhood of the nuclei and that thus a determining factor in 
the orientation of the cleavage surfaces would be introduced. The 
well-known facts as to the effect of acids and alkalies on the imbibition 
of water by colloids utilized by Pauli (25) in his surface tension theory 
of the contraction of striated muscle fibers and by Fischer (12), in his 
theory of oedema may have significance in connection with those 
processes which involve the exudation of water in the sporange. A 
localized production of acid in the colloidal spore-plasm involving 
differentiated capacity for the retention of water might determine 
the direction of the cleavage furrows. The cleavage planes would 
naturally follow zones of greatest water loss thus isolating such 
acid-containing areas. If the nuclei either by reason of their char- 
acteristic chemical content (nucleo-proteids, nucleic acid) or by the 
products of their metabolism could thus become centers of moisture 
