AND DEW BY THE GREEN PARTS OF PLANTS. 315 



be plunged into w* 

 seen. Moreover M 



■ 



oxygen ean readily be 



limb of an animal, to which it is obviously not comparable; for 

 there is no such mutual dependance between a shoot or a leaf and 

 the main stem as in the case of an animal's limb. The one can 

 be detached and made to strike root and grow into an independent 

 plant ; not so the other. 



All that can be called injurious to a shoot when detached for 

 experimental purposes lasting for a short time only, is that the 

 supply of water is cut off. The shoot may become flaccid and 

 slightly enfeebled ; but in no sense are its functions impaired. And 

 I maintain, making due allowance for that fact, whatever results 

 a cut shoot or detached leaf gives in the matter of absorption and 

 transpiration, they are legitimately applicable to a growing plant. 



Those who assert it to be otherwise must bear the burden of the 

 proof. 



M. Duchartre's experiments were made with plants growing in 

 pots, the latter being carefully protected from imbibing any 

 moisture by a mechanical contrivance. The plants thus prepared 

 were weighed at 6 or 6.30 p.m., then subjected all night to dew. 

 They were again weighed at 6 or 6.30 a.m. on the following morn- 

 ing, with the dew still upon them. The leaves were then carefully 

 wiped one by one till the whole plant was dry. It was then 

 again weighed ; and the result was that the weight was almost 

 exactly the same or more generally a little less than it was the 

 evening before. Duchartre consequently came to the conclusion 

 that in our climates dew is not absorbed directly by plants, but 

 that it contributes to their nutrition indirectly only, (1) by re- 

 ducing the nocturnal transpiration to nothing, and (2) by the in- 

 tervention of the soil, which absorbs the dew. 



The fundamental objection that I raise against his conclusion is 

 that he has not considered the difference that exists between the 

 statical or nearly statical conditions of the internal flow of water 

 in a plant at night, with the dynamical or active flow ever taking 

 place as soon as transpiration and evaporation are perfectly re- 

 sumed in sunlight and heat. 



He has shown it to be true, though not so absolutely as has 

 been often asserted, that transpiration is greatly checked when 

 the surfaces of the transpiring organs are thoroughly wetted, or 

 when in darkness. Darkness and superficial moisture combined, 

 as on a dewy night, must therefore reduce this vital act to a 



