52 ‘Dr. D. P. Gardner on the 
10. Several observations have been made on the gases contain- 
ed in the cavities of plants, by Priestly, Davy, Ferrand and Calvert, 
-Payen and others. But in all cases the collections have been in 
supernumerary organs, or such means have been taken for obtain- 
ing the gas as to interfere with the result. The examination has _ 
also been made without considering the effects of a porous epider- 
mis, and the internal changes going on in the plants. It is obvious 
that the internal atmosphere of a permeable body, freely in con- 
tact with air, and with the gases. of fluids or the soil, and which 
is moreover an apparatus of decomposition and- other chemical e. 
actions must be ever fluctuating. 'The presence of light, itsin+ 
tensity, and the structure of the soil are disturbing causes. 
» 11. Placing before me the above considerations, and the known 
fact that the gases evolved by growing plants differ in light and 
darkness, I considered in what way to obtain a knowledge of the 
normal atmosphere of active plants. It is not worthy of thought 
im investigating this question, whether the internal gases are sep- 
arated into spiral or laticiferous vessels, or insulated cellules; itis — 
probable there is an inner system of barriers, which in the higtier ia 
vegetation is necessary to produce particular results, but in the 
lower classes this is absent, and therefore we might infer that 
there is a common plant atmosphere as well as a peculiar combi- 
nation of gases within particular portions. 'The solution of the 
problem appears to rest in ‘obtaining the gas diffused throughout — 
plants whilst they are in a vigorous state, some time after the — 
sun has been acting on them, and without mutilating the speci- 
mens before use, as nearly every observer has done. 'The gas of | 
the plant shontd not be drawn out by the air-pump because the _ 
elastic fluids of the sap and of the closed vessels are obtained in 
this way and these are not sought after. 
12, For the purpose of satisfying these conditions, I stars ; 
ed in May, 1844, several young plants of Datura stramonium 
and blue grass (Poa pratensis) into small tumblers and allowed — 
them to remain three to six weeks before use, so as to be perfectly is 
vigorous. Having completed my arrangements for analyzing 
minute portions of gas, by means of a sliding-rod eudiometer, J 
proceeded in the experiments after the following manner. ‘The 
time of examination was about 11 4. m., after the plants had been 
prem ea (June.) Two or more — 
1g se the tumblers w eS 
a 2. 
sie ei ei a 
