492 POPULAR SCIENCE MONTHLY. 



PLANTS AS WATEE-CARRIERS. 



By Professor BYRON D. HALSTED, 



RUTGERS COLLEGE. 



A GIANT redwood, the monarch of the California forests, stands 

 -^-*- with its stem-tip three hundred and fifty feet above the soiL 

 From the surface of the millions of tender delicate leaves near the top 

 of the tree there are exhaled many gallons, perhaps barrels, of water 

 daily. The force required to make good this loss is, of course, equal to 

 that needed to raise the water through the three hundred feet or more 

 of vertical space. It is no wonder that the thoughtful person will 

 pause as he contemplates this exhibition of force. It makes no noise; 

 work is being done, but it is not easy to see how. 



Let us begin with the soil, as that is the source of the water supply 

 of plants, and briefly consider its constitution, texture and relations 

 to the problem of water-carrying. In other words, does soil carry 

 water and, if so, in what way is it conveyed ? Soil is rock that has been 

 broken into small pieces in one way or other, a refinement of rock, so 

 to speak, whether by frost, moving water or chemical action. For our 

 purpose soils, having many degrees of fineness, may be classified into 

 coarse, medium and fine. Coarse soil may be compared to masses of 

 cannon balls touching each other but with large spaces between them, 

 while the medium soil is similar to peas in piles, and the fine soil is like 

 clover seed. The chief difference is in the amount of surface exposed 

 by the particles which go to make up a definite portion of soil. 



The next point for us to consider is the capacity of soil for holding 

 moisture. Thrust the hand into a dish of water and upon removal it 

 will be wet, except any portion that has been coated with oil or similar 

 substance. In short, water will leave its own mass and adhere to the 

 surface of the hand. If the hand held a quantity of clean earth the latter 

 would likewise become wet. The amount of water that the soil will 

 hold depends upon the surface exposure of its particles. As this is an 

 exceedingly important point, permit me, at the risk of dealing largely 

 in dry figures but for explanation and proof, to draw upon some re- 

 sults given by Professor King in his charming book 'The Soil.' With 

 columns of sand ten feet long, the one with the grains averaging in 

 diameter 186/10,000 inch, after percolating for 111 days, contained 

 3.77 per cent, of water; the 73/10,000-inch grains retained 4.92 per 

 cent.; the 61/10,000-inch grains, 5.76 per cent, and the 45/10,000- 

 inch grains, 7.57 per cent. In other words, the smaller the size of the 



