THE RESPIRATION OF PLANTS. 71 



Still, with full-grown leaves in the open air, and with abundance 

 of light, we but rarely find them exhaling even a very small amount 

 of carbonic acid ; though as was shown by M. Corenwinder ten years 

 ago if we transfer them to a room lighted only by side-windows, and 

 to which the direct rays of the sun do not penetrate, they generally, 

 under these conditions, exhale carbonic acid in the daytime, the pro- 

 portion varying according to the nature of the plants, the weakness 

 of the diffused light, and the temperature. Of all the plants experi- 

 mented on in this way by M. Corenwinder, the common nettle appeared 

 to give out the largest amount of carbonic acid, when kept in a room. 



These facts M. Corenwinder announced ten years ago, but he did 

 not then venture an interpretation of them, as he does now. 



M. Boussingault has shown that leaves placed in a bell-glass con- 

 taining pure hydrogen mixed with a little carbonic acid, and kept in 

 an ill-lighted room, give off traces of oxygen. This proves that even 

 under the most unfavorable conditions the assimilation of carbon does 

 not entirely cease: this act is completely suspended only in total 

 darkness. 



Now, as it is likewise certain that, under the same conditions as to 

 light, leaves kept under a bell-glassy?^? with air give out carbonic 

 acid, and inhale oxygen, it follows inevitably, from these two classes 

 of observations, that the functions inherent in plants, respiration and 

 assimilation of carbon, are simultaneous; the latter function is, how- 

 ever, reduced to such a degree that it no longer completely masks the 

 effect of the former / in other words, the chlorophyll can no longer 

 absorb all the carbonic acid produced by respiration. 



Here, then, we have a fact analogous to that which we see in the 

 earliest stage of vegetation, with this difference, that in the case of the 

 bud the reducing action is insufficient, owing to the relative inferiority 

 of its carbonaceous matters, while in the other case the insufficiency 

 results from the reduction of their power. 



These facts are undoubtedly very strong arguments for the theory 

 of two simultaneous functions in leaves. M. Corenwinder still further 

 confirms it with sundry observations, which are easily made. 



Place perfectly green, full-grown maize-leaves under the bell-glass 

 of the apparatus already described, and it will be seen that in the day- 

 time they do not exhale the slightest trace of carbonic acid. If we 

 could deprive these leaves of their green matter, which to all intents 

 and purposes performs the assimilative function, we could doubtless 

 discover the other function which this conceals, viz., respiration. Now, 

 this very experiment Nature makes easy for us. As all are aware, 

 there is a species of maize with striped leaves, which often bears white 

 leaves without a trace of green. If we examine closely the striped 

 leaves, we shall see that their white portions have absolutely no chlo- 

 rophyll within. This is not the case with the leaves of a purple or of 

 a black color ; these, in addition to the coloring matter characteristic 



