Disease in plants / by H. Marshall Ward.

  • Ward, H. Marshall (Harry Marshall), 1854-1906
Date:
1901
Catalogue details

Licence: In copyright

Credit: Disease in plants / by H. Marshall Ward. Source: Wellcome Collection.

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    of the mineral, and Nobbe, in 1876, showed that the roots of seedlings reduce potassium perman- ganate, a fact which Molisch confirmed in 1887. The latter observer also proved that living root- hairs secrete substances which colour a solution of guaiacum blue, oxidise pyrogallic acid and other organic substances, and rendered it probable that they excrete some substance which inverts cane- sugar, and in some cases even small quantities of a diastatic enzyme. Molisch also confirmed an old observation, that roots excrete carbon-dioxide ; and he and Czapek showed that the root-hairs excrete acids more permanent in their nature than carbonic acid, and published a method for showing this by means of a dilute solution, slightly alkaline, of phenol- phthalein. Molisch declared that the substances secreted by root-hairs may even be observed, dissolved in drops which ooze from the surfaces of the root- hairs. That these root-excretions, and particularly the acids, may be of service in dissolving and render- ing more available various constituents of the soil is an obvious suggestion, and it is borne out by Sachs’ discovery of the corrosion of marble, and by Molisch’s observation that living roots slowly corrode ivory if continuously kept in contact with it. But a deeper insight into the physiology of these organs was only possible when the meaning of the phenomena of osmosis had been rendered