EFFECTS OF RAIN. 



123 



fibres which form the trunk of a tree is in proportion to the 

 number of leaves which that tree has borne, from which we 

 come to the conclusion that the size of the trunk of a tree 

 is the sum of all its branches. While all this is going on, 

 the cellular tissue of the downward part or radicle also 

 becomes developed and divides out into roots, on the surface 

 and at the extremities of which are minute cellular bodies 

 called "spongioles" (from their power of absorbing moisture), 

 which take up the fluid of the earth which surrounds them ; 

 this moisture ascends through the vessels of the plant till it 

 arrives at the surface of the leaves, where it is exposed to 

 the action of light and sunshine. The ascent of the moisture 

 of the earth was first correctly explained by Du Trochet, 

 and is owing to a peculiar 

 power which he discovered, 

 and which is called "Endos- 

 mose ; " this consists in the 

 tendency which a fluid has to 

 penetrate a membrane on the 

 other side of which is a fluid 

 of greater density than itself. 

 This may be seen by the follow- 

 ing experiment : obtain a piece 

 of glass tubing about a foot 

 long, having the end blown 

 out into the form of a bell, as 

 in fig. 7, tie a piece of bladder 

 over the expanded end and fill 

 it partly with syrup or gum- 

 water, so that this shall rise 

 in the stalk about an inch ; 

 place this in a glass of water 

 with the bladder downwards, 

 and the fluid will be seen slowly 



to rise in the stalk, so that in FIG> 7._ ENDO sMosB. 



perhaps an hour it will rise to 



the top. This apparatus resembles one of the spongioles at 

 the extremity of the fibre of a root. 



The rain falling through the air carries with it a certain 



