PLANTS AS WATER-CARRIERS. 493 



grains and the pores the greater the amount of water retained. With 

 soils of still smaller particles the water-holding power would be cor- 

 respondingly greater. 



If the soils are placed in long upright glass tubes and water is 

 added at the bottom, it will rise through the soil to the top. This 

 phenomenon of capillarity is best illustrated with tubes having bores 

 of varying diameter. The tables given us on this subject are to the 

 effect that, when an inch tube is plunged into a vessel of water, the 

 height of the water column in the tube above the general level is .054 

 inch; for a 1/10-inch bore .545 inch, 1/100-inch bore 5.456 inches and 

 for a 1/1,000-inch bore, 54.56 inches. While the actual surface pull of 

 the smallest tube is much less than that of the largest, it is through a 

 vastly greater distance and by a multiplication of the number of such 

 minute tubes in a given space that the greater lifting is brought 

 about. 



The soil itself, consisting of minute particles, admits of the capillary 

 action; for the pores, although not straight, extend in irregular lines 

 and permit the surface tension that is evident in fine tubes. This 

 lifting power of minute passageways is abundantly illustrated in the 

 everyday operations of crop-growing, and the skilful tiller makes 

 abundant use of it or checks it as best suits his purpose. If a dark soil 

 contains an abundance of light alkaline salt, it is possible that it may 

 have a white crust form upon the surface during a drought to be 

 carried back upon the falling of a substantial rain, and this rise and fall 

 may be repeated indefinitely as happens on some of our alkaline lands, 

 where the precipitation is light and vegetation scant. 



It has been shown that the soil, on account of its porosity, is able to 

 lift water through considerable distances, simply through the greater 

 pull of a solid for the liquid than the liquid has for its own particles. 

 The hand is wet by the water; a towel hung high with barely one 

 corner dipping into the basin may become wet throughout, and, by 

 evaporation, the dish may be pumped dry. 



Into this complex physical porous mixture, to the component par- 

 ticles of which a liquid adheres with such force as to be present when 

 even the air is dry, the plants establish themselves by means of their 

 tiny rootlets and the much more minute root hairs which, insinuating 

 themselves between the microscopic pebbles, become misshapen and con- 

 torted beyond all recognition of the simple vegetable cells out of which 

 they have grown. The movements of the water in the soil, whether to 

 the right or left, up or dovni, are governed, as has been shown, by the 

 law of surface attraction. When we come to the plant cell, the whole 

 physical basis is changed, and, among other things, we are brought 

 face to face with membranes of extreme thinness and delicacy, and, 

 more than all, with the living protoplasmic film. 



