66 RIcHARDS AND MacDouGaL 
the cells appeared quite normal. In CO the younger cells while 
alive were paler than the normal and the peripheral layer of motion- 
less protoplasm was enormously thick and apparently very much 
denser than in the usual condition. The chloroplasts were gorged 
with starch. 
As a result then of progress already made in our experiments 
it may be said definitely that carbon monoxide, which has been 
hitherto considered neutral and without influence on plants, is in 
effect highly toxic when used to replace, partially or entirely, the 
nitrogen of the atmosphere. The experiments have not yet yielded 
sufficient detail to allow any determination of the point at which it 
ceases to be toxic, or to determine whether or not, like carbon di- 
oxide, it stimulates growth when present in small proportions in 
the atmosphere. It has been shown, however, that a wide range 
of reaction to this substance is to be found among plants. 
The deleterious action of the carbon monoxide results in modi- 
fications, of the rate and amount of growth, of the differentiations 
of the primary tissues, and of the formation of chlorophyl. | 
Illuminating gas, containing proportions of carbon monoxide 
slightly above and below 40 per cent., affords, in addition to the 
toxic action of the carbon monoxide, the results of the action of 
other substances deleterious to the plant. 
The contents of this abstract will be published as soon as 
practicable, but the description of the details of the experimental 
tests and a consideration of the whole subject will await the con- 
clusion of the investigation. 
