CLEAVAGE IN DIDYMIUM MELANOSPERMUM 
(PERS) MACBR. 
R. A. Harper 
WITH plates' XI AND XII 
Many recent papers have confirmed the contention that cell 
division in the sporanges of algae and fungi is a process of progressive 
cleavage by surface furrows as against the older conception of simul- 
taneous division by cell plate formation. Still the unique type of cell 
division by repulsion of the coarser cell inclusions and their heaping 
up in neutral planes which delimit the oospheres, described by Farmer 
and Williams (ii) for the oogones of Fucus still remains unquestioned 
and little has been added to our knowledge of the mechanics of the 
cleavage process. The older authors were for the most part dominated 
in their descriptions of spore formation in sporanges, first by the 
erroneous theory of cell formation put forth by Schleiden, and later 
by the conceptions of cell plate formation derived from studies on 
the higher plants. This older literature has been several times ade- 
quately summarized and need not be referred to further here (15, 29). 
Timberlake (31) describes the swarm spore formation in Hydro- 
dictyon as taking place by means of furrows which cut in from both 
the plasma membrane and the tonoplastic surface of the primordial 
utricle. Klebs's (18) figures also certainly suggest that the division 
is a progressive process. 
Klebahn (17) speaks of the division of the oogonia in Sphaeroplea 
as a cleavage and his figure (no. 2) shows furrows cutting up the multi- 
nucleated oogone into the eggs. He does not describe the process of 
division in the antheridia. 
Swingle (29) has proved beyond question that in Rhizopus and 
in Phycomyces the cell division consists in a progressive cleavage by 
which the multinucleated spore-plasm is cut up into the definitive 
spores. In Rhizopus the furrows originate primarily from the periph- 
ery ; in Phycomyces they originate largely from vacuoles in the 
spore-plasm. The process in these forms is similar to that in the 
sporanges of Sporodinia and Pilobolus (16) but with striking and 
characteristic differences. 
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