54 Irrigation and Drainage 



stance in the economy of plant life, and large quantities of if are 

 used, but that it is so difficult to always procure enough that 

 nature has provided in the organization of the plant that none 

 be wasted unnecessarily. It must be very evident, also, that 

 whatever we may do, in our methods for growing crops, to keep 

 the plants so fully supplied with moisture that they shall be able 

 to utilize all the sunlight, by keeping their breathing pores 

 wide open, so that all air which can be used will be supplied, 

 must tend to give us larger yields. 



THE MECHANISM BY WHICH LAND PLANTS SUPPLY 

 THEMSELVES WITH MOISTURE 



So long as plants maintained a simple, or relatively few- celled 

 structure, and especially so long as they lived wholly or largely 

 immersed in water, it was an easy matter for them to be supplied 

 with as much water as they needed by simple diffusion and 

 osmosis, just as the dry bean, when put to soak, swells and 

 becomes turgid by the water which has been driven into its cellu- 

 lar structure under the ceaseless hammering impulses of heat. 

 But when the time came for plants to abandon the water and to 

 occupy the land with their varied forms, and especially when that 

 race began for free air and direct sunshine which led on from 

 herb to shrub, and through arborescent forms to the giant forest 

 trees, then it became necessary for that complex and wonderful 

 system of water-works which, with its intakes in the form of roots, 

 spread out in a comparatively dry, well -drained soil, is able to 

 gather from off the damp surfaces of soil grains and send to a 

 height of a hundred feet a stream which, when divided between 

 ten thousand leaves, shall yet have volume and pressure enough 

 to keep them turgid in a strong, drying wind and a hot sun. 

 Man, with his mechanical skill and inventive genius, has been 

 able to install pumping plants which can lift more water to a 

 greater height in a shorter time ; but to do this he has been 

 forced to statiort- himself by a running stream, or to import his 

 energy at a great cost ; while the land plant, independent of wind 



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