TRANSACTIONS OF SECTION B. 695 
This decomposing rice is then placed in water and exposed to the action of a 
yeast, which rapidly ferments the sugar, and the alcoholic saké results. 
So closely is the yeast associated with the Aspergillus, that, in practice, the 
alcoholic fermentation commences soon after the enzyme of the Aspergillus begins 
to hydrolyse the starch of the rice, and for some time a controversy existed as to 
whether the yeast was not really part of the life-history of the Aspergillus. Several 
observers have now shown, however, that we have here a striking case of symbiosis. 
On reviewing these examples, we shall find that very different degrees of associa- 
tion of the organisms are to be met with. 
At the one end of the series we find two organisms merely associated for a 
short time, e.g. bacilli and worms, bees and botrytis-spores, and, so far as we may 
speak of symbiosis at all in these cases, it is merely temporary or disjunctive. 
At the other end of the series we have a close permanent combination of the 
two organisms working in unison, e.g. the lichens and Winogradsky’s Closterium 
with its protective mantle of aérobic bacteria; also the ginger-beer plant and 
kephir. 
Put between these extremes it is possible to find all stages, the halfway house 
being met with in cases such as the saké ferment, where the Aspergillus evidently 
prepares the way for the Yeast. 
It has been proposed to apply the term Metadiosis to such cases, 
It must not be forgotten that there are extremes in the other direction, 
where one of the two associated organisms is injuring the other, as exemplified by 
many parasites, but these cases I leave out of account here. This state of affairs 
has been termed Antidiosis. 
It seems not impossible that the biological relationships of these cases one to 
another could be shown thus :— 
Antibiosis, Symbiosis, 
‘ 
Facultative parasitism. Meta-biosis. 
r A 
Ny / 
Disjunctive—association. 
The Physiology of Symbiosis. 
It will be an interesting exercise to see if we can get any further glimpses into 
the physiology of the phenomenon of Symbiosis. 
When we come to enquire as to the processes which lead to enhancement of 
the functional activity of one organism by another living symbiotically with 
it, the matter presents many difficulties ; for it is at the outset quite obvious that 
many things are possible, and soon becomes evident that a tangle of complexities 
lies before us, as always in the inter-relations between associated biological units, 
We need go no further than the examination of the possibilities in the inter- 
relations between a weed anda cultivated plant, or between two trees in a forest, 
for illustrations of this truth. 
Confining attention for the moment to closely associated symbionts, such as 
those composing a lichen, the ginger-beer plant, or a clump of symbiotic bacteria 
or fungi, researches have made it practically certain that the provision of definite 
food-materials by the one symbiont for the other may be an important factor; 
e.g. an alga supplies a fungus with carbohydrates, or a fungus converts starch 
into the fermentable sugars which the associated yeast needs. In other cases the 
advantage derived is one of protection from some injurious agent—e.g. the aérobie 
bacterium prevents the access of oxygen to the anaérobic one. But there is evi- 
dence which suggests that mere nutrition or protection is not the only or even the 
principal factor involved. It is well known that the products of fermentative 
