90 Effect of Manganese Gam/pounds 



III. Effect of Manganese Compounds on Certain of the 

 Lower Plants. 



The information on this point is exceedingly meagre, possibly 

 because of the diversion of general attention to the higher plants 

 in view of the commercial interests involved. 



Richards (1897) carried out experiments with various nutritive 

 media with the addition of certain metallic salts, including those of 

 zinc, iron, aluminium and manganese. The fungi tested were Asper- 

 gillus niger, Penicillium glaucum and Botrytis cinereA. His general 

 conclusion was that fiingi may be stimulated, though it must not be 

 concluded without further investigation that all fangi react in the 

 same degree to the same reagent, but this conclusion is traversed by 

 Loew and Sawa (1902). These writers state that fiingi are not stimu- 

 lated by manganese, and take this as a proof that the improvement in 

 the growth of phanerogams, induced by manganese compounds, is not 

 due to direct stimulation of the protoplasmic activity, but to some other 

 more obscure cause. 



IV. Physiological Considerations of Manganese Stimulation. 



The physiological cause of the stimulation exerted by manganese 

 compounds has raised much controversy. Loew and Sawa suggested 

 that the action of the sun's rays upon a normal plant puts a certain 

 check on growth, arising out of the action of certain noxious com- 

 pounds which they supposed to be produced in the cells imder the 

 influence of light. The stimulation of the manganese compounds may 

 be due to a supposed increase in the oxidising powers of the oxidising 

 enzjmies, so that destruction of the checking compounds can be accom- 

 plished as quickly as they are formed, so enabling growth to continue 

 more rapidly. 



Aso (1902) had previously stated that colorimetric tests for oxidising 

 enzymes indicate that the yellowish leaves from plants treated with 

 manganese compounds give reactions of higher intensity than the green 

 leaves from control plants, the difference between the reactions being 

 specially marked in barley, and less so in radish. 



Bertrand has devoted much time to the consideration of this and 

 allied problems. In 1897 (a, b, c) he proceeded to investigate the 

 essential nature of manganese in the economy of the plant, his 



