Lecture 5 — 107 — Artificial Media 



Conditions for the Growth of Plants in Artificial 

 Cultures : — Granted that plants can grow in a solu- 

 tion of simple inorganic salts, it is then necessary 

 to examine the factors of the solution environment 

 that must be favorably controlled to insure the growth 

 of the plant according to some preconceived idea of a 

 proper rate of development for the prevailing climatic 

 environment. In a previous lecture the suggestion 

 was advanced that it is not possible to designate some 

 one particular combination of salts as constituting a 

 "best" nutrient solution under all conditions. Among 

 other points, the rapid absorption of nutrient ions by 

 growing plants and the ensuing change in composition 

 of a nutrient solution were stressed as complicating 

 factors. We have in fact to deal in solution cultures 

 as in soils with a question of "supplying" power. 

 Obviously, even if the initial composition of the nu- 

 trient solution is the same, plant growth over an ex- 

 tended period of time may differ greatly depending 

 upon the initial volume of solution or on the number 

 of times the solution is changed. In early researches 

 on salt relations of plants investigated by water cul- 

 ture technique there was a tendency to overlook this 

 consideration. 



One of the requirements of the water-culture tech- 

 nique is to regulate the initial volume or the number 

 of changes of solution so that no nutrient ions fall 

 below a critical level of concentration unless it is the 

 purpose to induce a specific deficiency or to study 

 interrelations of ions without regard to maintained 

 supply. Very low concentrations, at least of mobile 

 ions like potassium, may suffice, if because either of 

 a large initial volume of solution or of frequent 

 changes, the solution never reaches a critical state of 

 depletion. In general, absorption curves for nutrient 

 ions show that relative to concentration, a much 

 greater proportion of ions is absorbed from a dilute 

 solution than from a more concentrated one. 



