4° 



osmotic action. In the ordinary case of osmosis above referred to, 

 there was a thick syrupy solution, viz., sugar, to account for it. 

 The ash, on analysis, is found to consist principally of inorganic 

 salts, such as chlorides and nitrates, and it was formerly thought 

 that this extraordinary osmotic action was due to their presence. 

 The presence of coloring matter and sugar will not account for 

 it, since these are only occasionally, not universally, present, 

 while the nitrates and chlorides are so ; but recent researches 

 have shown that these latter are present in too small quantity 

 to exercise this power, and that another explanation must be 

 sought. If we take a section of a plant and touch it with blue 

 litmus solution, we obtain distinctly red or acid reaction, for in 

 cutting the section we have ruptured a considerable number of 

 cells, and this acid fluid is in most instances the cell-sap. This 

 acid reaction is due to the presence of certain organic acids 

 formed as the result of the living activity of the protoplasm of 

 the cell, and not taken up from the exterior. They occur in 

 nearly all the cells of plants, and it seems probable, according 

 to De Vries, that they are the bodies to which the osmotic 

 action and properties are due, for if we neutralize the cell-sap 

 of cells they lose at the same time their osmotic properties, and 

 can no longer absorb the requisite amount of water to keep the 

 cell in the necessary degree of tension. 



And now, having got a correct and accurate idea of what a 

 vegetable cell is, and of the various properties of the several 

 constituent parts, we may go on to enquire the method in 

 which the first great movement of fluid in the plant takes place. 

 First, we have then to consider what is known as the rapid 

 movement of fluid in plants. This also possesses other names ; 

 it is known as the ascending current of the crude sap, or the 

 rise of the sap. Under this head there are several processes 

 included, which, for simplicity, it will be as well to consider 

 seriatim. 



First then Absorption — what is the exact method by which 

 plants absorb their nutriment ? If we take first the simplest 

 case, viz., that of a unicellular organism swimming freely in 

 water, we find that every part of the plant is equally adapted for 



