— The'Life of the Plant. — 159 
connection, but are isolated one from another, and the reason of 
the solid condition of a body is that its molecules have a mutual attrac- 
tion for one another; and the stronger this attraction, the more firm 
and solid is the body which they compose. Every molecule is in its 
natural state surrounded by a layer of water, so that they are com- 
pletely separated from one another on ail sides. Within certain limits 
a portion of their watery contents can be removed from organised 
structures ; or they can take up fresh quantities without being thereby 
destroyed or killed. Loss of water or desiccation causes a contraction, 
the absorption of water an increase or swelling of the body. The 
molecules of one and the same organised body separated by envelopes of 
water always differ chemically, so that molecules of a different chemical 
nature are found in the midst of and beside one another at every 
point that can be perceived by the microscope. 
THE MOVEMENT OF WATER IN PLANTS. 
It follows as a necessary consequence from the structure 
of organised bodies, that life is impossible in the most 
- minute particles of the plant without access of water. The 
plant also requires water for the formation of organic sub- 
stances out of the inorganic food-materials which it takes 
up ; and furthermore, for the solution of solid substances 
stored up in it, the zeserve-materials, which must be dis- 
solved and transported to other places, where they are con- 
sumed. In addition to this, delicate leaves, like those of 
most plants, lose in a short time a considerable portion of 
the water of their cell-sap by evaporation. In order to meet 
all these requirements, it 1s necessary that continuous cur- 
rents of tater should pass through the plant, and should 
be directed towards those parts where the plant requires it. 
Those currents.which subserve the processes of nutrition 
and growth must therefore move sometimes in an ascending, 
sometimes in a descending, and sometimes in a lateral direc- 
tion, while that which serves to replace the loss by evapora- 
tion is continually ascending from the roots. The water, 
therefore, which is sucked up by the root-hairs flows 
