611 
of Edinburgh, Session 1885-86. 
action and modes of reproduction. Thus, micrococci having the 
same appearance may have different effects. Cohn divides his 
genus, Micrococcus, into three physiological species — (1) Chromo- 
genie, (2) Zymogenic, (3) Pathogenic. He places the Micrococcus 
Vaccinse among the pathogenic micrococci, but the record of the 
cultivations just detailed shows that the vaccine organism is also 
chromogenic, so that it might equally well be classed among these 
coloured micrococci. At the same time, he admits that differences 
in arrangement and size are unreliable data upon which to found 
the classification of species. A necessity, therefore, arises for the 
acceptance to some extent of the theory of pleomorphism (Tulasne), 
i.e., that the same plant can occur under two or more forms, as well 
with respect to the organs of vegetation as to those of reproduction. 
Applying this theory to the bacteria, we find that a single species 
may show various forms in the course of its life-cycle. This has 
been shown by the researches of De Bary, Zopf, Dallinger, Douglas 
Cunningham, Ewart and Geddes, and others. 
The propagation of fungi takes place asexually in three ways — 
1 By free cell formation (asci, thecae, spore-pouches). 2. Constric- 
tion (basidians). 3. By cell-fission or gemmation. Spores are the 
chief means of the spread of fungi (Wagner). 
Surrounding media modify the form and mode of fructification of 
fungi, some increasing and others diminishing spore-formation, or 
we may have the fungus dividing into yeast forms. Schwann, 
Pasteur, and others consider the yeast fungi as organisms sui generis , 
arising in fermentable liquids from their own specific germs. 
Hallier, Hoffmann, and others consider that they are only condi- 
tions, especially of mould fungi occurring in fermentable liquids, 
particularly the spore forms, which fructify in the atmosphere in 
other forms. They originate likewise from spores or from yeast cells 
themselves when they reach a liquid. Hoffmann thinks that the 
genera of Schizomycetes, described by Ehrenberg, Pasteur, &c., pass 
into one another, peculiarities which are to be held as characteristic 
of the species, and which change in the course of development 
according to the change in the external conditions of life (Wagner). 
As we have seen, Cohn maintains that such genera are distinct 
throughout life. Species may show various sizes and different pig- 
ments besides differing in their effects. Zopf is a warm supporter of 
