Rothamsted Symposium on Trace Elements 80 



the rate of elongation of 40 to 50%. These figures are computed 

 graphically from the growth curves of the cells. The elongation 

 with manganese also starts earlier and this causes the reduction 

 found in the length of the meristem. 



By some prolonged tests it was observed that the cell growth 

 in the absence of manganese was even increased, and the cells 

 obtained unusual lengths of more than 300[jl. In one experiment, 

 on four consecutive days, the following figures were noted for the 

 cell length of the newly formed cells: — 



Dxy — Mn +Mn 



Without manganese the growth is irregular. In spite of the 

 abnormally increased cell lengths in this case, the rate of elonga- 

 tion was always higher vidth manganese, but the stretching ceased 

 earlier. Without manganese it continued for a longer time but 

 at a slower rate. A rapid increment in net length of the excised 

 roots does not necessarily imply a favourable progress of growth. 



Summarizing, we have found, hitherto, that manganese, al- 

 ready during the first 24 hours, causes a more rapid start of the 

 elongation of the cells and a more rapid elongation. It seems as 

 if the period of cell elongation went more rapidly in the presence 

 of manganese, but the net result as to cell and root length may be 

 variable, depending upon known or uncontrolled factors. 



This action of manganese agrees pardy with the one obtained 

 with nitrate, in as far as nitrate also enhances the rate of the cell 

 elongation. But nitrate does not cause the elongation to start 

 earlier, nor does it shorten the period of cell elongation, so that the 

 picture we receive is not identical with the one outlined before. 

 It may be that manganese has also other influences, or that nitrate 

 is acting pardy by itself, without reduction, by increasing the ion 

 concentration of the roots. We cannot say more than that the 

 results do not contradict our assumption that manganese regulates 

 nitrate assimilation. 



The following figures show the combined action of manganese 



