——— \ a 
Physical Structure of Planis. 57 
body instead of carrying it into the sap of the plant; the gas thus 
liberated being nearly insoluble in the remaining fluid, rose 
through it into the upper part of the receiver. It is even prob- 
able that the roots gave off no gas whatever from the sap. 
25. The experiments show that plants do not merely absorb 
the gases dissolved in water, as is usually imagined, but~ that 
their action is regulated by internal functions, for during night or 
darkness, the water, with its gaseous contents undisturbed, is ab- 
sorbed, but during the active condition of vegetation a selection 
is made of carbonic acid chiefly, and that oxygen is also ab- 
sorbed, whereas in all probability every molecule of nitrogen is 
rejected. 
IV. The absorption of Gases by Plants is a result of their porosity. 
26. We are now in possession of sufficient data to state the 
case, A porous system lies between two media and contains a 
certain internal atmosphere; the gaseous composition of these 
three are as follows :— 
; The air. The plant gas. The water gas. 
Carbonic acid, - 0:05 0-00 30-0 
Oxygen, » 20-80 13-25 22-0 
Nitrogen, 79°15 86°75 48-0 
100: 100- 100- 
If the mixture designated the plant gas, were confined within 
an extremely delicate caoutchouc bag and surrounded by either 
water gas or atmospheric air, it would soon be disturbed by 
penetration, nitrogen would be slowly eliminated and carbonic 
acid and oxygen absorbed. The rapidity of the movement would 
depend on the gas and also the character of the membrane. So 
much for the physical consequences ; we now proceed to examine 
what really takes place in the case of plants. igRoD 
27. The action of the roots on the water gas existing in the 
soil, and represented by that in pump-water, is given at length in 
the last division of the memoir; as there are no experiments on 
the subject accessible to me I must advance my own in confirm- 
ation of the correctness of the physical theory. In M. Boussin- 
gault’s Economie Rurale, it is stated that M. Piobert found that 
Toots absorbed nitrogen, but as I have not seen any evidence of | 
this I canno: admit it in opposition to my experiments. 
Stconp Series, Vol. II, No. 4:—July, 1846. ick ceakaas 
