CLEAVAGE IN DIDYMIUM MELANOSPERMUM (PERS.) MACBR. 1 29 
Lowenthal (20) describes zoospore formation in Zygorhynchus as 
simply the bounding off of a portion of protoplasm about each nucleus; 
but his figures show no stages in the process nor evidence as to how it 
takes place. 
Kusano (19) claims to be able to distinguish two types of cell 
division in Synchytrium puerariae. The first type is a progressive 
cleavage by broad furrows leading to the formation of multinucleated 
sporanges. In the second type the sporanges are formed "by the 
precipitation of partitions in the compact cytoplasmic mass." Kus- 
ano's figure 6 probably represents young sporanges after cleavage is 
completed and growth has begun though he argues against this inter- 
pretation. It is an old and familiar observation which Wager (34) 
re-emphasizes that after cleavage is complete the spores may swell and 
grow so as to press upon each other to the extent of making the lines 
which mark their boundaries very inconspicuous, especially in living 
material. It is this condition which has apparently deceived Kusano. 
Kusano further erroneously identifies his second type of division with 
that described by Timberlake for Hydrodictyon. As noted above, 
however, Timberlake describes the cell division in Hydrodictyon as 
taking place by furrowing and as progressive. For Rhodochytrium, 
Griggs (13) says, like Kusano, that he observed both progressive 
cleavage by surface furrows and simultaneous segmentation and adds 
that the former was infrequent. 
Barrett (4) describes the segmentation of the protoplasm in the 
sporanges of Blastocladia as proceeding from the periphery inward, 
much as I have described for Synchytrium decipiens, but he adds that 
the lines of division are first recognized as rows of granules which are 
at first more or less indefinite but which become more and more 
apparent till they are seen to outline the spores. There can be little 
doubt, however, as his figures 30 and 31 suggest, that what he describes 
as rows of granules are in reality cleavage furrows. For the sporanges 
of Olpidiopsis, Barrett (3) speaks of the division of the protoplasm as 
involving the formation of spore centers and states that as far as he 
could determine the fragmentation was simultaneous throughout the 
sporange much as described by Dangeard for Synchytrium taraxaci. 
He seems, however, in this case not to have really found the cleav^e 
stages ; for his figure 39 certainly represents a condition after cleavage is 
complete, and his figure 38, as he states, represents a stage in which 
segmentation has not yet begun. It is interesting to note that Bally 
