44 PKOPAGATIOlf OF PLANTS. 



in their passage through the cells, and the chemical, 

 mechanical and vital forces are all engaged in this work. 

 There is a thorough filtering of the solutions as absorbed, 

 else the crude sap or liquid would often remain colored 

 as it passes upward ; but this seldom occurs, even when 

 the roots are submerged in highly colored, and what are 

 generally considered, very nutritious fluids, as, for in- \ 

 stance, the drainings of a manure heap, and from other 

 similar vegetable matter. Still, roots do sometimes ab- 

 sorb vegetable dyes, as has been shown in various experi- 

 ments with extract of Madder and the juices of the Poke- 

 berry, but in no instance on record has the coloring 

 matter produced any permanent efEect on the plant or 

 become hereditary, and it is seldom that the added color 

 can be traced upward in the cells to any considerable 

 distance ; showing that the liquid as filtered through 

 the cell- walls, as it passes from one to another, soon 

 parts with any uncongenial foreign materials which may 

 be present ; at least the attempt is made to do this, and 

 in case of failure, as with poisonous gases, the plant is 

 killed. While the living cells may reject coloring matter 

 and fail to retain it, the dead tissues of plants are readily 

 colored by absorption — a purely mechanical operation — as 

 constantly practised by the manufacturer of microscopic 

 slides, the stainers of wood, and dyers of vegetable fab- 

 rics in general. 



It is quite evident that whatever is absorbed by the 

 roots is subjected to unceasing changes and transforma- 

 tions, the result of the action of chemical and vital forces 

 about which there is yet much to be learned. 



Eoots that grow in the dark possess somewhat different 

 functions from those growing in the light ; at least the 

 chemical changes which take place in them are different. 

 We know that roots differ very widely, not only in their 

 forms and structure, but in their habits as well. Some 

 appear to require resistance, like those of trees which 



