1] MICROSCOPIC PLANTS. 13 
we can easily find out what gas it is. We test it, and 
find it to be carbonic acid gas. How isthis? There 
was no carbonic acid gas in the fluid, We analyse 
the fluid again, and find that the sugar has dis- 
appeared. And so we proceed with our experiments ; 
and, in the end, see clearly that the oxygen has been 
taken out of the sugar by the Torula, and the car- 
bonic acid gas set free; in fact, it has been feeding 
upon the sugar. Now Protococcus is able to get its 
food from the carbonic acid gas, and sets free orygen. 
Torula can’t obtain its oxygen from carbonic acid 
gas, or it would have multiplied in the rain-water. 
There is evidently some remarkable difference in 
these plants. Protococcus possesses chlorophyll, by 
means of which it is able—under the influence of 
sunlight—to decompose carbonic acid gas. Torula 
does zo¢ possess chlorophyll, and therefore has to get 
its food from a substance already formed by plants, 
This it finds in the sugar, which contains both carbon 
and oxygen. Torula exists as well in the dark as 
in the light; Protococcus cannot exist in the dark. 
If we apply a small quantity of iodine to both, we 
find that Torula remains unchanged, while Proto- 
coccus turns blue, This denotes that it contains’ 
starch,a substance peculiar to green plants; on the 
other hand, Torula agrees with the Fumg7 in possess- 
ing neither starch nor chlorophyll, and in being 
independent of light. Protococcus we may take as 
a simple type of the green plants, and Torula of the 
Fungi. 
If we take a tiny drop of the yeast on the head 
of a pin, touch a glass slide with it, and, carefully 
