Lecture 5 



— 115 — 



Artificial Media 



tomato plants growing in a culture solution is depen- 

 dent on a liberal supply of oxygen to the roots and 

 upon prevention of too high CO2 concentration in 

 the root environment. This objective may be achieved 

 by the rapid passage of a current of air around the 

 roots of each plant. A sand culture flushed daily with 



pH 5 



pH 6 



Ca-?- 20 80 280 



20 80 280 



20 80 280 



Textfigure 33. — Diagrammatic illustration of yields of roots 

 and shoots of tomato plants grown at several pH values of 

 nutrient solutions and with variation in calcium concentrations. 

 Calcium concentrations in parts per million of solution. (From 

 Arnon and Johnson, 1942). 



nutrient solution likewise provides a suitably aerated 

 medium. Our specially aerated water cultures pro- 

 duced plants of somewhat larger yield of fruit than 

 we obtained from even an exceptionally favorable 

 and heavily fertilized soil, when cultures were ar- 

 ranged side by side in the greenhouse.* The assump- 



*The orders of magnitude of yields were, however, the 

 same. It may be noted also that a porous bed superimposed 

 over a tank of culture solution affords good, although not 

 necessarily optimal, aeration. 



