Rothamsted Symposium on Trace Elements 78 



assimilation. It may also be possible, by means of a morpholo- 

 genetical study, to locate the action of manganese at some special 

 point in the metabolism of the cell. 



In order to approach this problem we first had to study the 

 morphological action of nitrate. This was done by determining 

 the rates of cell multiplication and cell elongation of the epidermis 

 of wheat roots. The methods and some results have already been 

 published (Burstrom 1947: K. Fysiogr. Sallsk. Forhandl. Vol. 

 17). A reduction in the nitrate concentration below its optimum 

 has a very characteristic effect on root growth. A decreasing sup- 

 ply causes, of course, a reduction in the root length, which is due 

 to a greatly decreased rate of cell elongation. As a result the 

 fully developed, mature cells are short, but there is at first little 

 reduction in the number of cells. This means that the rate of 

 cell multiplication continues, and that the optimum nitrate concen- 

 tration, for this part of the growth process, must be lower than that 

 for the cell elongation. This nitrate action is almost the reverse 

 of that of phosphorus. A decreasing supply of phosphorus pri- 

 marily affects meristematic growth but not cell stretching. I men- 

 tion these circumstances in order to show that it is possible, on a 

 large amount of material, to distinguish experimentally between 

 these two phases of growth, thereby making a quantitative analy- 

 sis of the growth process. 



Experiments performed in order to illustrate the action of 

 manganese in the same way meet, of course, with greater difficul- 

 ties. We started from the assumption that if there is really some 

 direct influence of manganese on nitrate transformation, the mor- 

 phological effect must reveal itself in short time tests, even if the 

 effect is not so prominent as when nitrate itself is withheld from 

 the roots. In experiments of long duration, complications may 

 arise, due to the adaptation to manganese deficiency, as assumed 

 by NoACK, and to the indirect effect of manganese. 



We experimented with attached as well as detached roots of 

 wheat seedlings which had been grown for 4 to 6 days in manga- 

 nese-free solutions under constant light and temperature condi- 

 tions. In neither case did we obtain any regular or significant 

 change in the length of the roots if manganese was supplied for up 

 to three days, but the morphology of the roots was markedly af- 

 fected by addition of manganese in amounts down to 1 p.p.m. 



Attached roots, of course, reacted less than excised roots. Very 

 clear results were obtained when all roots were removed from the 



