VERTICAL FARMING 



23 



derived from the soil where it may have accumulated from arti- 

 ficial supplies, from the action of bacteria, or from the decay 

 of organic matter. The relative amounts of these elements 

 demanded by different plants varies considerably, as some re- 

 quire a large supply of one food element while others can grow 

 well with much less of it. 



Only the root hairs, the most delicate 

 part of the root system, can absorb foods. 

 These are tiny threads growing out from 

 the roots just back of the tiny feelers or 

 root tips that thrust themselves through the 

 soil. The walls of these root hairs are 

 very thin and absorb the soil solution direct 

 as they lie in close touch with the soil par- 

 ticles covered with their thin coat of u Min- 

 eral Soup." These dissolved mineral foods 

 then pass on into the circulating system of 

 the plants as sap, and are carried up to the 

 leaves. The sap in conjunction with the 

 carbonic acid taken in by the leaves then 

 forms the starch, sugar and similar com- 

 pounds of the plant and the excess of water 

 is lost through the leaves. The amount of 

 water evaporated in this way is enormous. 

 It has been found on experimentation that 

 it requires from 200 to more than 600 pounds 

 of water, passing through a plant in this 

 way, to make one pound of dry crop. 

 These large amounts of evaporated water 

 show how necessary it is to keep the soil in 

 such a condition that it will absorb the maximum amount of 

 rainfall and hold it to supply the growing crop. It is also 

 necessary that these tiny root hairs, that are so small that it 

 would take 300 or more laid side by side to cover an inch in 

 width, be able to creep and grow always deeper and further 

 into the soil, unhindered by impacted soil, hardpan, or other 

 obstructions. 



ROOT HAIRS 



