REPRODUCTION IN LOWER PLANT LIFE. 99 
instance of the formation of flagellate zoospores ; the only 
known mode of propagation is by some form of division or 
fission. In some of the lowest genera of Cyanophycez we 
have, notwithstanding the absence of motile swarm-cells, 
a more or less well-marked power of apparently spontane- 
ous motion. In Microcystis (fig. 2). a minute organism 
common in stagnant water, and in Aphanothece, which often 
forms large gelatinous masses on wet rocks or on submerg- 
ed plants, this is confined to a swarming motion of the 
rudimentary blue-green cells or pseudocysts within their 
common envelope. In Celospherium, (fig. 3) a beautiful 
and common object in bog-pools, nearly spherical, but with 
the blue-green pseudocysts projecting above the surface of 
the globe, the whole organism moves about with consider- 
able rapidity with a kind of rolling motion. It should be 
mentioned with regard to this lowest order of Cyanophy- 
cex, the Chroococcaces, that some algologists who have 
devoted to them much time and very careful observation, 
have adopted the view, not only that many of the genera 
hitherto regarded as distinct are genetically connected 
with one another as different states or vegetative condi- 
tions of the same organism ; but that most, if not all of 
them are, so to speak, embryonal stages in the development 
of Alge belonging to a much higher type. ILcrocystis has 
even been regarded as a resting stage of Euglena. 
It is instructive to notice how, in the higher families 
of the Cyanophycez, that motility is localised, which, in 
the Chroococcacee, is characteristic of the entire organism. 
In these higher filiform families of blue-green Schizophy- 
cex, the Nostocacez, Rivulariacese, Scytonemaceze, aud 
Oscillariaceee, the ordinary mode of propagation is by 
means of hormogones, strings composed of a small num- 
ber of cells which detach themselves from the rest of the 
filament, escape from their mucilaginous envelope, move 
