CHAPTER II 



METHODS OF INVESTIGATING MICRO- 

 NUTRIENT PROBLEMS 



1. The Purification of Materials used 

 in Culture Experiments 



The existence of the micro -nutrients raises a number of pro- 

 blems which can only be solved after the development of 

 methods designed specially to deal with them. In the first 

 place the question inevitably arises as to how we can be certain 

 that any particular element is really essential or not. This is 

 obviously a problem of mineral nutrition requiring immediate 

 solution; it is clearly an essential preliminary for all investiga- 

 tions on the micro -nutrients that we should know what these are. 



It has already been pointed out that the essentiality of the 

 micro -nutrients for plant development was overlooked for half 

 a century simply because an adequate supply of them was 

 introduced into the culture (1) from the seed from which the 

 plant developed, (2) from impurities present in the water and 

 salts used in preparing the culture solutions, and (3) by solution 

 from the vessels used to hold the culture solutions. Hence the 

 problem of determining the micro -nutrients clearly resolves 

 itself into devising means for preventing the introduction of 

 micro -nutrients from these three sources. If this can be done 

 the effect of the absence or presence of any particular element 

 in the culture medium can then be determined for a wide range 

 of plant species. 



The prevention of the introduction of any particular elements 

 from the seed used for the cultures is perhaps scarcely possible. 

 But when the seed is small the amount of any micro -nutrient 

 present in it is likely to be negligible, and when the seed is large 

 the amount introduced can often be considerably reduced by 

 removal of the cotyledons from the seedling as soon as the latter 

 is established. Reference has already been made to Lipman's 

 method of meeting the difficulty in his experiments with buck- 

 wheat, in which seed was used from plants grown in culture 



