io6 Marshall Ward. — On the Characters , or 
Van Tieghem, and others, has culminated in the modern 
partial school of Zopf. It should be noted, however, that 
this series of observers has already undergone an important 
differentiation along two more or less diverging lines of 
thought: some of them, influenced by the writings of Naegeli, 
Billroth, and Zopf especially, have declared emphatically 
against the systematists, in so far that they have either 
denied the existence of species altogether among Schizomy- 
cetes, or have at least claimed that as the polymorphy of 
these organisms is now shown to be so marked — and it must 
be admitted that polymorphy, as measured by the Cohn- 
Ehrenberg standard, is very marked — species cannot be 
defined by the' morphological and developmental characters 
of the Schizomycetes. 
The others, comprising Beyerinck, Kurth, Cienkowski, 
Winogradsky, Klein, &c., remaining more faithful to the 
cautious utterances of Cohn and De Bary on this point of 
polymorphy, have satisfied themselves with declaring, or 
implying, more or less clearly, that, while polymorphy cannot 
be denied and should not be under-estimated, the difficulty 
of finding diagnostic morphological characters is after all a 
relative one, largely due to the minuteness of the organisms, 
and the few and simple differential features that they possess ; 
or at least that they exhibit under our microscopes. 
This double set, constituting a school, if we so choose to 
put it, of botanists, have undoubtedly done wonders during 
the last decade. It is only necessary to mention De Bary’s 
study of Bacillus Megaterium , Prazmowsky’s and Van 
Tieghem’s of Clostridium butyricum and Leuconostoc , Klein’s 
on the spores of Bacilli, Brefeld’s work on Bacillus subtilis, 
KurtlVs on Bacterium Zopfii , and Photobacteria , Wino- 
gradsky’s on Sulphur-bacteria and Nitromonas , Lankester’s 
and Zopf’s on Cohnia ( Clathrocystis ) roseo-persicina , Billet’s 
on Cladothrix , Beyerinck’s on Bacillus cyano- fuscus, and very 
many others, to see what enormous strides have been made 
in our knowledge of the forms and evolution of Schizomy- 
cetes during the period referred to, and what a weighty mass 
