10 



open among the loosely thrown upcast, and although these 

 diminish a good deal by pressure of the superabundant 

 material, yet the air they contained forces its way into the 

 microscopic interstices between particles far smaller than 

 grains of sand. 



So much for the air- supply demanded by the root 

 respiration. Let us consider the water supply. It is 

 unfortunately the current belief that trees must have 

 water given to them much in the same way as one waters 

 a horse. Either whole bucketsful are poured in at the base 

 of the trunk, or a stream is turned on to flood its surround- 

 ings. This is in direct opposition to the natural way trees 

 take up their water supply. "It is characteristic of the 

 mode of life of land-plants that they only flourish, as a 

 rule, when their roots are evenly distributed throughout a 

 soil that is relatively dry, and only partially flooded with 

 water."* The practice of agriculture bears testimony to 

 this fact in that damp low-lying lands are made highly 

 fertile by an adequate drainage which renders them 

 relatively dry. The culture of plants in greenhouses teaches 

 that land plants rooted in pots very easily perish if they 

 are watered too often, and one of the first lessons a garden 

 apprentice receives is " to keep his watering can quiet." 

 Land plants and particularly trees, carry on their root- 

 functions continuously only when the soil surrounding them 

 is relatively poor in water. A complete saturation must 

 be very brief and soon relieved by draining away, or else 

 it acts injuriously. 



12. Let us consider how the enormous losses of water by 

 daily transpiration from the leaves are made good by im- 

 bibition from soil, not wet, but only just perceptibly moist 

 to the touch, and therefore in the best possible condition 

 for sustaining healthy root-growth. Every minute particle 

 of earth, even down to those too small for distinct" vision, 

 is enveloped in a thin film of adherent water held fast by 

 surface attraction, almost as if it had been dipped in water 

 and brought out wet. Where particles by reason of their 

 angular shape happen to fit closely together, the attractions 

 combine to hold a thicker watery layer. The remaining 



* Sachs. Vorlesun gen, XV. Engl. Transl. p. 265. 



