Thus it appears that such lower organisms as yeast, lactic ferment and Aspergillus niger are remarkably indifferent to the action of boric acid, as is shown by the fact that the toxic dose is remarkably high, while stimulation effects cannot be observed even in the presence of the smallest quantities yet tried.
Conclusion.
Boric acid is less harmful to the growth of higher plants than are the compounds of copper, zinc, and arsenic. Evidence exists that below a certain limit of concentration boron exercises a favourable influence upon plant growth, encouraging the formation of stronger roots and shoots. This stimulation is more strongly marked with some species than with others, peas responding more readily than barley to the action of boric acid. Fungi are very indifferent to boron, whether it is present in large or small quantities, and there is evidence to show that certain of the green algae can also withstand large quantities of it.
CHAPTER VII
EFFECT OF MANGANESE COMPOUNDS
I. Presence of Manganese in Plants
The presence of manganese as a constituent of plant tissues has been known for many years, and in view of the close association between iron and manganese it was natural that the early investigators should seek for the latter element. [De Saussure (1804)] gives one of the earliest references to manganese in plant ash, stating that it occurs in the seeds in less great proportion than in the stems, and also that the leaves of trees contain less in autumn than in spring. At first oxides of iron and manganese were put together as “metallic oxides” and little or no attempt was made to separate them so as to get an idea of their relative abundance. [John (1814)] gives a number of rough analyses of plants and indicates the presence of manganese in many plants, including Solanum tuberosum, Brassica oleracea viridis L., Conium maculatum, Aesculus (in outer bark), and Arundo Sacchar. No further references presented themselves until 1847, as probably manganese was overlooked and always classed with iron in any analyses made during that time. [Kane (1847)] found traces of manganese in the ashes of some samples of flax, but none in others, and examinations of the soils on which the plants were grown gave similar results. [Mayer and Brazier (1849)] confirmed this result. [Herapath (1849)] analysed the ashes of various culinary vegetables, finding manganese in cauliflowers, swede turnips, beetroot, and in one variety of potato (Forty fold).
[Malaguti and Durocher (1858)] tried to investigate the matter quantitatively. The oxides of iron, manganese, and aluminium were all classed together, and the mean percentage of the three varied from ·85%–5·06% according to the varieties of plants concerned, Cruciferae possessing least and Leguminosae most. Different mean results with the same plant were obtained from different soils.
[Wolff (1871)] made other quantitative analyses including Trapa natans (·15% Mn3O4), Acorus Calamus (1·52% Mn3O4), Alnus incana (trace–·73% Mn3O4), Pyrus communis (2·15% Mn3O4). Many other plants were mentioned by Wolff as containing manganese.
[Campani (1876)] found manganese in ash by a method in which it was detected as phosphate of manganese, and he claimed to be the first to discover manganese in wheat ash. [Warden (1878)] found traces of Mn3O4 in the ash of opium from Behar.