376 Harper.—Sexual Reproduction in Pyronema 
not, so far as we know, in the nuclei, which are all at least 
potentially equivalent in their capacity to transmit the 
hereditary characters of the organism or to influence the 
metabolism, since so far as known any of these nuclei may 
be used to form a reproductive spore, and by the streaming 
of the cytoplasm they are carried successively to rhizoid, stem, 
and leaf. 
These organisms would be qui e as difficult to include in 
the category of cells, if they were uninucleate, if that were 
conceivable. They represent the extremes of differentiation 
yet discovered in a structure enclosed by a common cell wall 
and plasma-membrane, but it is quite as difficult to consider 
them from the standpoint of tissues since in their metabolism 
and irritability, they are by no means compounds made up 
of equal and co-ordinate units. On the whole it does less 
violence to the facts to class them as cells than in any other 
category yet proposed. There is nothing in our conception 
of a cell that is negatived by the assumption of the differen¬ 
tiation of its parts into organs of nutrition, organs for attach¬ 
ment, reproduction, &c. 
In the case of all such multinucleated cells as are combined 
in filaments or other structures the interpretation is much 
easier. The red Algae afford exceedingly interesting evidence 
against the possibility of separating uninucleated from multi¬ 
nucleated cells, since in immediate connexion with each other 
in the same thallus we have vegetative cells that are regularly 
uninucleated, and others that are just as regularly multi¬ 
nucleated. It is plainly doing violence to the most obvious 
relationships to call the one type a cell and the other a 
tissue. 
The multinucleated vegetative cells and sexual cells of 
Pyronema fall in this same class, and if we compare in detail 
these coenocytic cells with uninucleated cells and with tissues 
composed of the latter, it will be seen that the coenocyte is 
a single cell in all its essential properties and not a compound. 
Anatomically and morphologically the cell is a mass of 
protoplasm enclosed by a continuous semi-permeable and 
