confluens and the Morphology of the Ascocarp. 375 
already known, must be thoroughly investigated and com¬ 
pared. 
The motive to such investigations lies, however, not so 
much in the desire to further pile up evidence on the question 
of the sexuality of the initial cells of the different ascus-fruits 
as in the hope that thereby further light may be thrown 
on the more general questions as to the structure and functions 
of the cell. The peculiar types of cell-division, fertilization, 
&c., found in the group may be expected to afford useful 
data for the solution of general physiological problems. One 
of the most interesting features in the reproduction of Pyro- 
nema is the fact that we have in it a case of the fusion of 
multinucleated sexual cells. The hyphal cells of Pyronema are 
regularly multinucleate, and, as has been shown, the oogonia 
and antheridia contain a large and variable number of nuclei 
at all stages in their development. In the fusion of these 
cells the nuclei fuse in pairs so that the general result, so far 
as the nuclei are concerned, does not differ from what is found 
in sexual fusions ordinarily. 
An interesting question arises, however, as to the nature of 
such multinucleated sexual cells. Is the oogonium for instance 
to be regarded as a mass of oogonia whose cell walls have 
been obliterated or have never existed, or is it to be regarded 
as a single cell ? Is a ‘ coenocyte 5 a cell or a tissue ? It is not 
merely a question of names, since from both the morphological 
and physiological standpoints our conceptions of the cell and 
of the tissue differ very widely, and it is worth while to 
determine, if possible, which of these types the ‘ coenocyte ’ 
resembles more nearly. The suggestion of the energide 
doctrine by Sachs has been taken up uncritically and carried 
too far by many. The cell is not necessarily a uninucleated 
mass of protoplasm. Whether the conception of the cell 
should be so extended as to include such differentiated 
structures as Caulerpa and Bryopsis is perhaps not so plain. 
Still the difficulties involved in regarding them as cells are 
not due to the fact that they are multinucleated. The 
differentiation shown by these plants is in the cytoplasm and 
