656 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Algae and Infusoria. Freshwater diatoms can, however, thrive in water 
at the freezing point, but the freezing of the medium exercises a fatal 
effect upon them. Desiccation is fatal to diatoms, and they are not 
able, as has been asserted by some writers, to return to life after having 
been completely dried up. The most favourable rays of light for the 
cultivation of diatoms are the yellow ; next the blue and green ; the 
white and red rays are inactive. Freshwater diatoms should, therefore, 
be cultivated behind yellow glass. A temperature above 45° C. is 
rapidly fatal to their development. 
Classification of Diatoms.* — Dr. J. Pelletan proposes the classifica- 
tion of Diatoms into 2 sub-orders, Placochromese and Coccochromese, 
9 families, and 24 tribes. The Placochromeae consist of the families 
Cymbellaceae (Achnantheae, Gomphonemeae, and Cymbellese), Nitzschi- 
aceae (Nitzschieae), and Naviculaceae (Amphiproreae, Pleurosigmeas, 
Naviculeae, Surirelleae, Synedreas, and Eunotieae) ; the Coccochromeae of 
the Tabellariacese (Tabellarieae, Licmophoreae, and Rhizosolenieae), 
Fragilariaceae (Fragilarieae, Plagiogrammeae, Uand Trachysphenieae), 
Chaetoceraceae (Chaetocereae), Biddulphiaceae (Biddulphieae), Coscino- 
discaceae (Eupodisceae, Heliopelteae, Asterolampreae, and Coscinodisceae), 
and Melosiraceae (Xanthopyxideae and Melosireae). The further 
classification into tribes and genera follows. 
Cymbellaceae.f — Dr. J. Pelletan classifies the genera belonging to 
this family of diatoms into three tribes, viz.: — (1) Cymbelleae, a 
single plate of endochrome resting by its middle on one of the sides 
of the zone, and by its margins on the other side ; frustules unsym- 
metrical, with a convex dorsal and a straight or concave ventral 
side: — Cocconema, Ampliora , Cymbella, Epithemia , Encyonema ; (2) 
Gomphonemeae, a single plate of endochrome, of which the middle 
rests on one side of the zone, its margins on the other side ; frustules 
cuneiform: — Rho'icosplienia , Gomphonema ; (3) Achnantheae, a single 
plate of endochrome lying on the internal face of the upper or dorsal 
valve ; frustules curved or geniculate, generally epiphytic ; valves 
unlike ; raphe and nodules on the lower or ventral valve ; a pseudo- 
raphe, but usually no nodules, on the upper valve : — Cocconeis , Cyclo- 
phora , Cymhosira , Achnanthes , Achnanthidimn^ Gephyria , Eupleuria, Rhoi- 
coneis. 
M. P. Petit appends a different classification of the Achnantheae, 
comprising the same genera, with the exception of Achnanthidium. 
p. Schizomycetes. 
Classification of Schizomycetes. :|: — In discussing the present chaotic 
condition of the classification of Schizomycetes, Prof. II. M. Ward sug- 
gests that two main causes have tended to bring about this undesirable 
end, the first being that the botanists have confined themselves too 
closely to the morphological characteristics, while the bacteriologists 
have laid too much stress on the behaviour of the species towards the 
media. The various systems of classification in vogue are then passed 
* Journ. de Micrographie, xvi. (1892) pp. 57-8, 89-90. f Tom. cit., pp. 89-90. 
X Ann. of Bot., r vi. (1892) pp. 103-44. 
