_ or two water vacuoles ; each cell is about ;j, mm. in 
diameter ; the cells are in twos or threes, or frequently 
run together in strings, like a breaking up chain of gem- 
a 
table, such as a slice of carrot. 
and, like many other innocent fungi, it has had the credit 
of producing the Asiatic cholera, and rejoices, among 
other synonyms, in the name of Cylindrotenium cholere. 
- In solutions containing sugar we often find a mul- 
titude of round or oval cells, precisely resembling the cells 
which I have already described in other fungi ; a delicate 
_ membrane surrounding a mass of protoplasm, with one 
mules of a MZucor. These are the well-known Saccharo- 
myces cerevisi@, the yeast fungus. In multiplying, which 
they do with extraordinary rapidity, these yeast cells throw 
up irregularly from the surface one or more buds, much as 
other fungi produce conidia. These separate, and in 
‘turn multiply in the same way; but the last stage in 
the development of this fungus is one which brings 
it into the regular series of ascomycetous fungi, the 
formation of regular asci or utricles, which corre- 
spond exactly with the asci of Aspergillus. These 
contain four to eight spores, which, when placed under 
favourable circumstances, vegetate in the ordinary way. 
It is after the sprouting of fresh yeast has taken place for 
some time in a fermenting solution, and has become 
languid, that the formation of asci begins, and we can 
produce them artificially by taking yeast out of a solution 
of sugar, and placing it upon the surface of a fresh vege- 
From yeast we pass toa 
‘series of very nearly-allied forms, which, as we shall see 
hereafter, perform a somewhat different function, the 
difference altering their value prodigiously in human 
economy. In sour wine and beer, in the process of 
the manufacture of vinegar, and wherever we have 
_ what is called the acetous fermentation, minute bodies 
_ swarm in the solution which closely resemble yeast, 
differing chiefly in the smaller size of the cells. Some- 
times these appear in pairs, sometimes single, and some- 
times as little vibrating jointed rods. The best known, 
and perhaps the most mischievous, are the mould fungus 
of sour wine, Mycoderma vini, and the “ mother of yine- 
_ gar,” Mycoderma aceti. These are called Mycoderma 
_ because the cells are entangled in a sort of slimy film, 
_. From these we pass to another class of bodies 
scarcely distinguishable from them morphologically, but 
‘ 
_ usually even still more minute, which are universally 
_ spread wherever putrefactive decomposition is going on, 
Bacteria and Vibriones, These and the lactic acid, and 
_ butyric acid yeast-fungi cannot, however, so far as we at 
present know, be ranged with the Ascomyceti, but must 
_ be placed in another group, for which the term Schyzomy- 
_ cetihas been proposed parallel with the Nostocs among 
_ Confervoids. 
Having thus given a very brief sketch of the morphology 
of this singular group of beings, I should wish to make one 
or two general remarks, In the first place, with De Bary, 
I would exhort you to remember that these beings whose 
morphology we have been discussing, although they are 
very small, are nevertheless A/avés, each going through its 
* own life-history, and presenting at different periods, and in 
connection with the performance of the different functions 
of its life, definite forms like every other plant. You know 
_ how to think about peas and beans, oats and rye-grass, and 
after sowing a crop of peas you never jgo and watch it, 
NATURE 
79 
wondering whether it will come up peas or barley. You 
never watch the growth of a turnip, expecting to find it 
gradually turning into a carrot ; and you never set aside 
a bowl of gruel and wait till acorns come in it, and 
wonder whether, if they do come, they will sprout into 
cabbages or hedgehogs; and yet there are slight 
difficulties in the study of the plants which we 
have bzen describing which have led men apparently 
otherwise well instructed to write reams of trash, gravely 
advocating absurdities of essentially the same order. 
These difficulties are in the first place that these plants 
are extremely minute, and their investigation requires great 
skill in manipulation, and great practice. Again, they are 
enormously abundant, and their multiplying germs of all 
kinds are so minute and all-pervading that it requires the 
utmost experimental dexterity to separate them, to sow 
them, and still more to exclude them. 
select and sow one species, ten to one the seed is mixed 
with the seeds of a multitude of weeds, and if during the 
process we allow the most indirect and instantaneous 
communication with the open air, instantly the enemy sows 
tares among our wheat, and one of these, probably more 
vigorous than the others, in the course of an hour has cut 
short its weak struggle for life. Then the form of these 
plants requires very careful study—some parts of them, such 
as the universally diffused mycelium, are undistinguishable 
in different species ; and so are the gemmules, conidia, and 
spores examined singly. _It is often only when the 
entire ‘ fructification ” is’ present that distinguishing 
characteristics exist which one can grasp. Then there is 
another difficulty—most of these plants present some form 
of the singular phenomenon of pleomorphy ; perhaps not | 
more so than other plants, but slight differences in form 
tell greatly in such simple and critical organisms. They 
present different forms at different periods of growth, and 
under slightly different circumstances, It is therefore not 
the appearance of the particular mould-fungus at any one 
time which we have to consider, but its life history. In 
this, however, as in all other such cases, we must apply 
the ordinary rules of experience and common sense. 
A plant of rhubarb, pink and clear, drawn up and forced 
in a can, is very unlike the same plant grown outside, 
with great green leaves and giving off a multitude of 
multiplying buds from its root crown; and without 
some little knowledge and experience it would be 
difficult to identify either of these with the plant in the 
autumn in its reproductive stage, shooting up its stately 
axis with its myriad of white feathery flowers. The diffi- 
culties in studying the small fungi are very great, but a 
few men, not perhaps very many, are capable of dealing 
with such difficulties, and by the application of the 
methods and reasoning of such men as De Bary, Pasteur, 
Lister, Burdon Sanderson, and Hartley, men trained in 
skilful investigation and accurate thought, the wild mis- 
conceptions which have lately gathered about the whole 
subject are fast passing away. 
I will now turn for a few minutes from the morpho- 
logical to the physiological part of the question, from the 
researches of M. De Bary to those of M. Pasteur. 
These active little scavengers, the microscopic fungi, 
live upon and in, spread their mycelium over and through, 
and flourish on the surface of decaying vegetable and 
animal matter; but it is not the decay which produces 
If we attempt to — 
