Importance of Cleanliness to Plants. 53 



tical gardener. We must, however, confess that we do not 

 feel altogether satisfied with some of the experiments, be- 

 cause we are not quite sure that it is fair to compare the 

 endosmosis or passage of water through a membrane, with 

 the gaseous transpiration which would occur through the 

 same membrane ; because the conditions most favorable to 

 the one are not necessarily also always those best suited to 

 the other. The experiments of the author do not bear upon 

 this question ; he merely shows that such vegetable tissue is 

 really permeable to carbonic acid, but does not by direct 

 experiment prove that this permeability is increased in any 

 definite ratio by washing. The author endeavors to prove 

 that carbonic acid gas is able to pass through the cuticle 

 of plants which have no stomata, by referring to the growth 

 of water-plants, which are without them ; and by an exper- 

 iment in which a portion of lime-water was enclosed in a 

 tube, the end of which was covered with a small piece of 

 such a membrane, and the tube then plunged for some hours 

 in an atmosphere of carbonic acid ; under these circumstances 

 the gas penetrated the membrane and rendered the lime- 

 water turbid. This experiment, however, is by no means 

 quite unexceptionable, because the question is not whether 

 pure carbonic acid will pass through the membrane and mix 

 with common air on the other side, but rather, whether 

 common air, containing 1 per cent, of carbonic acid, will 

 so pass through to mix with air containing no carbonic 

 acid. It is evident that the gradual filling up of the pores 

 with oleaginous or resinous matter, which destroys the power 

 of permitting endosmosis, does not necessarily also prevent 

 the cuticle from absorbing carbonic acid ; and, indeed. M. 

 Garreau says this himself, for he observes that a cuticle, which 

 has lost the power of transmitting water, may still be per- 

 meable to that gas. 



The second division of the paper contains a very valuable 

 and careful series of experiments on the evaporation of water 

 from the two surfaces of the leaf, and on the emission of 

 carbonic acid gas from leaves. In those experiments leaves 

 growing on healthy plants were selected, and a circular por- 

 tion enclosed between two closely fitting glass receivers, so 



