Importance of Cleanliness to Plants. 51 



A fortnight ago we briefly mentioned M. Garreau's very 

 curious experiments on the perspiration of plants ; we shall 

 now redeem the promise we then gave, by describing his 

 experiments more in detail, so that our readers may be in a 

 position to judge for themselves of the value of his conclu- 

 sions. M. Garreau's object, in the first place, was to ascer- 

 tain the ratio in which the cuticle and covering membrane 

 of plants is able to absorb or give out gaseous matters, what 

 differences exist between the same membrane on the various 

 parts of a given plant, and how these diff'erences are modified 

 by circumstances. The first series of experiments were 

 made to measure the real porosity of the epidermis, by as- 

 certaining the rate at which endosmosis takes place through 

 it, between various dissimilar fluids. Small portions of the 

 epidermis of diflferent plants, carefully prepared, were ce- 

 mented at the end of glass tubes ; a weak solution of sugar 

 was then poured into the tube, the lower end of which was 

 thus closed by the film of vegetable membrane, and the tube 

 was then immersed for a given number of hours in some 

 other liquid, after which the quantity of the latter, drawn 

 through the membranes by endosmosis, was carefully meas- 

 ured. 



The result of these experiments showed that the epidermis 

 of old leaves permitted little or no endosmosis, whilst that 

 of young leaves allowed it to a very sensible degree ; a fact 

 apparently caused by the considerable quantity of oleaginous 

 matter, which covers and impregnates the epidermis of the 

 former. On comparing together the epidermis taken from 

 different parts of the same leaf, it was found that it vai'ied 

 considerably in its relation to this passage of fluid ; the epi- 

 dermis of the nerves, and of the lower part of the leaves, 

 nearest to the leaf-stalk, being those which permitted it most 

 freely. An epidermis, which does not allow of endosmosis 

 in its natural state, becomes permeable to liquids, Avhen it 

 has been washed with ether, solution of soap, or in some 

 cases even with distilled water alone. These effects are 

 quite independent of the action of the stomata, and may be 

 observed quite as well with a membrane wholly destitute of 



