79 Burstrom: Manganese and Roots 



seedling, except one of the first two adventitious roots, and when 

 the shoot was cut off, at the beginning of the experiment, a Htde 

 above its basis. The test plant then consisted of a single root 

 attached to a piece of stem of a few mm length. Wholly isolated 

 roots grow very slowly, owdng to a lack of some unknown factor 

 of a probably hormonal nature, but if the shoot basis is left on, 

 growth continues at an almost normal rate, for some time, if carbo- 

 hydrates and other nutrients are supplied externally. The roots 

 are then rather sensitive to external conditions. 



Good results were also obtained with wholly isolated roots. I 

 must admit, that we did not succeed, in every instance, in ob- 

 taining an effect of manganese on such roots in 24 hour tests, but 

 usually we did, and then the roots always reacted in the same 

 manner. The first thing we observed was that the growing point 

 was shortened if the roots obtained manganese. Observed under 

 the microscope, we saw that the meristem is rather sharply set off 

 from the zone of elongation, and the length of the growing point, 

 before the start of the elongation, can be determined very ac- 

 curately. This proved to be distincdy shorter (up to 20%) in the 

 roots supplied with manganese. Further it was almost constantly 

 found that the mature epidermal cells of these roots were signifi- 

 cantly longer than those without manganese. The absolute length 

 of the full-grown cells varies very much and depends upon age and 

 nutrient status in general, but the manganese effect shows consist- 

 endy. Some figures may be given: — 



— Mn +Mn 



cell length n 



excised roots 127 ± 2 152 + 3 



attached roots 174 ±5 220+5 



249 + 5 315 + 5 



The last pair of figures refers to roots with unusually long cells. 

 The differences seldom exceed 25% but are highly significant. 

 These two observations, according to which the meristem is 

 shortened and the cell length increased, were taken as a starting 

 point for a detailed examination of the manganese action. 



It appeared that the real rate of cell elongation was always 

 much higher in the manganese roots and much more than was 

 to be expected from the differences in the final cell lengths. Such 

 a difference of 15 to 25% usually corresponded to a difference in 



