78 VEGETABLE ORGANOGRAPHY. 



bears the stomata must always be applied to the liquid : 

 so that they appear to be, in this case, absorbing organs. 

 However, when tliis experiment is performed with a 

 coloured fluid, the colouring particles never penetrate 

 the leaf ; whence it will be, perhaps, more exact to con- 

 clude, that if the leaves, supplied with water upon the 

 surface which is provided with stomata, preserve them- 

 selves fresh, this is only because the contact of the water 

 arrests their perspiration : this is illustrated artificially 

 in the state of a fleshy fruit, which, not having any 

 stomata, remains fresh for several weeks, or even 

 months. 



I think, then, in conclusion — 1st, that the customary 

 use of the stomata is for perspiring water, which must 

 be distinguished from simple evaporation ; — 2d, that it 

 is not impossible that they may also serve, in some cases, 

 for absorption ; but that the experiments are all ex- 

 plained pretty well by the hygroscopicity of the tissue ; 

 — 3d, that it is equally possible that they absorb water 

 during the night, but that the experiments are not suffi- 

 ciently multiplied to enable us to assert it. 



Independently of the stomata, wliich are quite visible, 

 it is probable that the surface of plants is pierced through 

 with imperceptible pores : these might appear, after the 

 progress of vegetation, to exist in the external walls of 

 the cellules, or on the cuticle, but so small that the 

 strongest microscopes cannot make them perceptible; 

 and they are only supposed to exist fr'om the physio- 

 logical phenomena which take place. Thus, when we 

 expose to the air a part of a plant which we know from 

 observation to be devoid of every other kind of pore, we 

 do not fail to remark that it graduaDy loses a little of its 

 weight, and that, consequently, the fluids which it 

 contains are found to have escaped : if we place [in 

 water a piece of the tissue of a Moss, which we know 



