Bristol, — Life-history and Cytology of Chlorochytrium grande. 1 2 1 
develops into a permanent spherical stopper of cellulose ; in Endosphaera 
it dies away, and very soon no trace of it can be detected. 
These two distinctions would seem to be far too unimportant to 
constitute generic characters, though they might possibly be used to 
differentiate between two species of the same genus. 
Again, Borzi admits that the zoogonidangia and zoogonidia of Centro * 
sphaera (1883) are identical with those of Scotinosphaera , Klebs (1881), but 
he separates the two genera because in Centrosphaera propagation takes 
place both by aplanospores and by zoogonidia, while in Scotinosphaera only 
propagation by means of zoogonidia has been observed. If the difference of 
habitat of these two genera be considered, the difference in their life-history 
may be explained as an adaptation to environment. Centrosphaera , Borzi, 
is able to multiply by means of aplanospores within the thalloid colonies of 
Lyngbya Phormidium , since the developing cells are able to make room for 
themselves by separating the Lyngbya filaments which are not united 
to form a compact tissue ; it is only comparatively rarely that zoogonidia 
are formed and escape to establish further centres of growth in other parts 
of the thallus. In Scotinosphaera , Klebs, however, which grows within the 
leaves of Hypnnm and of Lemna trisulca , aplanospore-formation would be 
disadvantageous on account of the difficulty which would be experienced by 
the mass of cells growing together within the relatively compact and 
inseparable tissue of the host. Zoogonidia, on the contrary, are able to 
distribute themselves- and to develop independently of one another. It 
would therefore seem better to consider that Scotinosphaera , Klebs, was 
originally identical with Centrosphaera , Borzi, but that, having acquired 
a truly endophytic habit, it has lost the power of aplanospore-formation. 
The absence of aplanospores in Chlorochytrium , Cohn, and Endosphaera, , 
Klebs, may perhaps be accounted for in the same way. 
A very intimate connexion between Scotinosphaera , Klebs, and Chloro- 
chytrium , Cohn, can be established through certain species of Chlorochytrium , 
notably through C. Knyanum , Cohn, and C. pallidum , Klebs, in which 
propagation takes place only by means of asexual zoogonidia. In these 
two species the life-history is identical with that of Scotinosphaera , and there 
seems to be no real reason why two generic names should be used for algae 
so very much alike. The conjugation of the zoogonidia in Chlorochytrium 
Lemnae is considered to be a case of gamogenesis and not a true sexual 
fusion, hence its occurrence has not been considered sufficient grounds for 
separating this species from those in which no conjugation takes place. 
This discussion indicates that a simplification of these genera would 
not only be more convenient for purposes of identification, but would also 
be more correct. The genus Endosphaera , Klebs (1881), should certainly 
be considered as synonymous with Chlorochytrhim , Cohn (1874), while the 
striking resemblances between Scotinosphaera , Klebs (1881), and Centro - 
