CYANOPHYCE 251 
like a true nucleus, and it has not been observed 
to display karyokinesis. Vacuoles do not appear 
ordinarily in the young cells, but with age, obscura- 
tion of light, or other unfavourable conditions, they 
arise and occupy a considerable part of the cell. It 
is not known, however, whether these vacuoles con- 
tain a cell-sap like those of other plants. Glycogen 
has been determined as present in the cells, but not 
starch. 
If we consider the close relationship of the 
Cyanophycee to the Bacteria, it is not strange that 
theories of their polymorphism have arisen. It has 
been supposed for example that forms like those of 
Chroococcacce: are often stages in the development of 
the higher Cyanophycece, and there are sufficient re- 
semblances to give colour to such a view. But there 
is no more proof of it than this slight ground of 
speculation, except the equally slender support de- 
rived from the fact that the forms frequently grow in 
the same places. It requires actual observation of 
development to establish such a matter. 
NosTOCACE. 
This order is distinguished from the Chroococcaceee 
by its multicellular thallus, and by the production of 
hormogonia, formed by the fragmentation of the 
filaments into mobile segments. The whole of a cell 
row is called a trichome, and the trichome with its 
envelope, which may be gelatinous, or even almost 
cartilaginous in consistence, is called the filament. 
