48 



THE LIFE OF THE PLANT 



Physics teaches us that particles of matter are 

 endowed with motion, that we do not know any matter 

 without motion. This motion is most clearly manifested 

 in fluids, and more especially in the gaseous state of 

 matter. Particles of gaseous matter are endowed with 

 rapid motion : they tend to disperse until they fill up 

 all spaces unoccupied by them ; this goes on until they 

 are equally distributed everywhere throughout the region 

 accessible to them. 



This capacity, this tendency of matter to spread in 

 space, is called diffusion. It is a simple matter to prove 

 the existence of the phenomena of diffusion, especially 

 in respect of gaseous and volatile substances. We have 

 only to sprinkle a few drops of ether to smell it in an 

 instant not only in the immediate neighbourhood but 

 also in the remotest corners of the room. The ether 

 has changed into vapour, and that vapour has 

 distributed itself throughout the whole room. The 

 diffusion of liquids is also easily demonstrated. I only 

 need to remind you of the probably well-known experi- 

 ment with water and wine. We gently pour some 

 claret on to the surface of water, and notice that the 

 liquids form two distinct layers ; 

 but Httle by httle the sharp 

 boundary between them disappears, 

 the wine permeates the water and 

 the water the wine, so that both 

 liquids mingle together. We can 

 perform here a similar but still more 

 striking experiment (fig. i6). Here 

 are two almost colourless liquids 

 which, when poured into each other, 

 produce a blood-red liquid. We 

 pour the denser of the two liquids 

 into this long, narrow beaker, then 

 with care the lighter one on the top of it. A narrow 

 layer of red solution appears between them; but in time 



Fig. i6. 



