ELEMKNTS or STRnrTPRAf. BOTANY. 



101 



a very curious process, the liquids absorbed by tho root 

 pass from cell to cell, though each is (pute enclosed, 

 until they reach the leaves, where the elaboration is 

 performed. Tlie process is carried on under the law, 

 that if two liquids of ditYoreut density be separated by 

 a thin or porous diaphragm, they will permeate tho 

 diaphragm, and change places with greater or less 

 rapidity according to circumstances, the liquid of less 

 density penetrating the diaiihragni more rai>idly than 

 the other. The cells of plants, as wo have said, contain 

 dense liquid matter. Tho moisture present in tho soil, 

 and in contact with the tender root-hairs (which are 

 made up of cells, you will remember), being i>f less den- 

 sity than the contents of the cells, flows into them, and 

 is then passed on from cell to cell on the same princi- 

 ple. The supply of assimilated matter is thus renewed 

 as fast as it is appropriated by the newly divided and 

 growing cells. 



IGG. If a plant, daring its existence, simply multiplies 

 its cells in this way, it can of course only bo a mass of 

 cellular tissue as long as it lives. But wc Kce every- 

 where about us plants, such as trees and shrubs, whose 

 stems are extremely firm and enduring. How do these 

 stems dltfer from those of tender herbs'? llow d) they 

 differ from the soft parts of the plants to which they 

 themselves belong '? A moment's consideration will 

 make it evident that, as every plant begins with a single 

 cell, and increases by successive multiplications of it, 

 every part of the plant must at some time have beer, 

 composed cf cellular tissue, just as the newer portions 

 are at present. The cells of those paits winch are no 



