MANUFACTURE OF ORGANIC FOOD 45 



in accordance with the physical law of osmosis. The 

 soil water contains about T V per cent, or less of mineral 

 matter in solution, whilst the fluid in the vacuole 

 of the root-hair may contain as much as 2 or 3 per 

 cent, of solid in solution. Physicists tell us that if 

 an organic membrane and the cell-wall is such a 

 membrane separates two fluids of different density, 

 both of which are capable of passing through it, the 

 less dense solution will 

 pass through with 

 greater rapidity into 

 the more dense, than 

 the more dense into 

 the less dense, and 

 hence the very dilute 

 solution in the soil 

 forces its way into 

 the interior of the 

 root-hairs. This entry 

 of a more dilute solu- 

 tion renders the cell 

 contents less dense than 

 those of the cell next 

 further inwards, and consequently a further flow from 

 the outer to the inner cell occurs. This, however, 

 will result in an increase in the density of the outer 

 cell, permitting of the entry of more of the dilute solu- 

 tion from without. In this way a constant stream 

 is set up from the soil outside to the interior of the 

 root, where the solution enters the vascular system 

 and is conducted upwards to the stem and distributed 

 to all parts of the leaf. The solution that reaches the 

 leaf is much too dilute for the chloroplastids to 

 operate upon, so that arrangements must be made 

 for its concentration by evaporation of the excess 



FIG. 17. Root-hairs, with soil par- 

 ticles attached. ( x 250. ) 



