5A | Dr. D. P. Gardner on. the. 
zine, of gas obtained from grass by the hr is precisely - M 
same as in the second examination. 
_ 15. In these measures we discover a wihissicibie uniformity . 
not only in the same species but in both plants. The mean of 
the six examinations with Datura gives an internal atmosphere of 
nitrogen 87-0, oxygen 12:5 percent cent., and the four with grass 
a mean of nitrogen 85:5, oxygen 14:5, or a mean of the whole we 
equal to nitrogen 86°75, orygen 13:25. This we. therefore as- 
sume as the normal or usual plant atmosphere at 11-to 124.) 
and. wasps weorous existence m the presence of bright comme d 
light. e 
16. Iti is distinctly to be understood that the pases or conde ‘ 
tionally normal atmosphere is perpetually changing, and is true — 
only for the time and place. In my preparatory examination of 
the subject I measured the internal gas of a specimen of grass as 
nitrogen 84'6, oxygen 13-0, carbonic acid 2-4 per cent., but over- _ 
looked at the time the circumstances of the analysis. — Messrs. — 
Calvert and Ferrand. give, as the composition of the. gas in the i 
hollow stems of Phytolacea decandria at night, sieniseiee 7645 
oxygen 20-6, carbonic acid 3-0 per cent. : a 
Ti. The. action of Roots on the Gases of the Soil Fluid. 
} At ‘The roots of plants present an absorbent surface which is ‘ 
probably little less than that of the leaves; a knowledge of their _ 
action is therefore indispensable toa proper understanding of the 
physical structure of plants. On this point nothing can bede- 
rived from the labors of others except that De Candolle (Physiol — 
ogie, t. i, p: 248) asserts that uninjured roots exhale no gas either — 
in light or darkness. Theoretically it is admitted by most phys 
iologists that the entrance of fluids into plants by their roots isa 
process of endosmosis, but in regard to elastic matters we ate 
left to infer that such find entrance as happen to be dissolved in 
the liquids of the soil, since no direct examination of this ee | 
has ever been made. | 
18. This inference that all the gases dissolved in the soil fiuid ‘2 
penetrate into the interior of plants, can only be admitted under ~ 
limited cireumstances. Wherever the sap is already saturated 
with a given gas, further quantities will not be received; and | 
again, the fluids of ES ERE NEN opposed to the — 
£ he. - samge ov ap nee ere t capacity of the 
Sa 
é e *% 
reuet Tis 
