112 Otis F. Curtis 



then suspended on a netting at the surface of the Hquid. The treatment 

 had no apparent effect on the percentage of germination; neither was 

 stimulation obtained when the seeds were soaked for twenty-four hours 

 and then suspended over distilled water. The authors explain the 

 stimulation as due to an enzymatic effect of the coUoidal suspension on 

 the reserve food in the seed. They believe that it is purely a catalytic 

 effect of suspended particles, as the metals were not taken up by the 

 plant and the strength of the suspension was not diminished. They state 

 that the stimulation could not have been due to substances in solution, 

 for if the colloids were precipitated by the addition of an electrolyte the 

 effect was nullified. It seems strange that the authors should explain 

 the stimulation as due to the enzymatic effect of the suspension on the 

 reserve food, when the stimulant was not absorbed by the plant and 

 when no effect was produced if, after soaking, the seeds were suspended 

 over distilled water. They did find a much increased root growth, and 

 it would seem probable that this increased growth, with the resulting use 

 of soluble food materials, might indirectly increase the rate of digestion 

 by removing the products of digestion. 



Brenchley (1910) found that root development of barley is stimulated 

 when manganese sulfate is added to the nutrient solution. 



In the Hawaii station report for 1910, Wilcox (1911) records results 

 obtained by planting various types of crops on the manganiferous soils. 

 He states that corn, rice, and other cereals, tobacco, cotton, legumes, 

 garden vegetables, and fruit trees, all showed more or less of the charac- 

 teristic yellowing of the tops, but the root systems were peculiar in that 

 the root length and the fineness of smaU roots were strikingly greater 

 than is found in root systems in ordinary soils. Wilcox says: "Apparently 

 the extreme fineness of the roots is due to the lack of resistance which 

 they meet in penetrating manganiferous soUs." 



Bertrand (1911) reports an increase in weight of roots of sugar beets, 

 and also an increase in the percentage of sugar, as resulting from the 

 addition of manganese compounds to the soil. He explains the stimu- 

 lation as due to the increased oxidase activity with the resulting increase 

 in respiration. In earlier publications (1896 and 1897) he showed that 

 manganese is an active principle in various plant oxidases, especially 

 laccase. 



