39 Arnon: Criteria of Essentiality 



Points from Discussion of Paper hy Prof. Arnon 



Dr, Brenchley:— 



If Professor Arnon has proved that any micro-nutrient is es- 

 sential for any one or more plants, does he consider that that in- 

 dicates that the element concerned is essential for all plants? 



Prof. Wallace:— 



In trace element cultures the risk of contamination of trace ele- 

 ments arises during the later stages of experiments due to accumu- 

 lation of elements from the use of the large quantities of water 

 which are necessary. This may result in deficiency conditions 

 ceasing to exist in a given technique. 



Prof. Nemec:— 



Have attempts been made to determine whether it is necessary 

 that every cell in the plant gets at least one molecule of every mi- 

 croelement? If it should be so, then it could be possible to assume 

 that the molecule is a constituent of the hypothetical sensitive 

 point of the cell. The necessity that every cell must get at least 

 one molecule of a trace element would give the lower limit for 

 further trace elements. 



