26 MINERAL SALTS ABSORPTION IN PLANTS 



3. Apparatus 



Various sizes and shapes of vessels are used to hold the experi- 

 mental medium, depending on the plant material under investigation. 

 Experiments may be performed on small amounts of tissue immersed 

 in as little as 3 ml of liquid, or, on a larger scale, whole plants may 

 be placed with their roots in 10 1. or more of solution. In any case, 

 when solution cultures are employed, arrangements must generally 

 be made to maintain the absorbing tissues at a constant temperature, 

 and to supply adequate aeration. Aeration is usually achieved either 

 by bubbling air through the solutions, or, when small volumes are 

 involved, by mechanical shaking. 



It is usual to employ a finite amount of medium and to arrange 

 the ratio of tissue to volume of medium in such a way that a 

 sufficiently small, but measurable, amount of salt is absorbed 

 during the experimental period. If the medium becomes too 

 depleted, salt concentration may become a limiting factor, and mask 

 other factors under investigation. In prolonged experiments where 

 it is desirable to prevent the medium from becoming much depleted 

 a flowing solution technique may be used. Here medium is allowed 

 to flow over the tissue or round the plant roots at a rate such that 

 the solution emerging still contains a large part of the salt originally 

 present. The rate of uptake of salt by the tissue can then be 

 calculated from the decrease in concentration if the rate of flow is 

 known. Details of such an apparatus were described by Van den 

 Honert (1933), and by Becking (1956). 



For further reading 



Hewitt, E. J. (1952). Sand and water culture methods used in the study of 

 plant nutrition. Tech. Comm. 22, Commonwealth Bur. Hort. and Plantation 

 Crops, East Mailing, Kent. 



