Inorganic Plant Poisons And Stimulants - free ebook by Winifred Elsie Brenchley

INORGANIC PLANT POISONS AND STIMULANTS

BY WINIFRED E. BRENCHLEY, D.Sc., F.L.S. Fellow of University College, London (Rothamsted Experimental Station) Cambridge: at the University Press 1914 Cambridge: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS...

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PREFACE

During the last century great and widespread changes have been made in agricultural practice—changes largely associated with the increase in the use of artificial fertilisers as supplements to the bulky organic manures which had hitherto been used. The value of certain chemical compounds as artificial manures is fully recognised, yet many attempts are being made to prove the value of other substances for the same purpose, with a view to increase in efficiency and decrease in cost. The interest i

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CHAPTER I INTRODUCTION

Ever since the physiological side of botany began to emerge from obscurity, the question of the relation between the nutrition and the growth of the plant has occupied a foremost position. All kinds of theories, both probable and improbable, have been held as to the way in which plants obtain the various components of their foods. But quite early in the history of the subject it was acknowledged that the soil was the source of the mineral constituents of the plant food, and that the roots were t

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I. Discussion of Methods.

In the course of the scattered investigations on plant poisons and stimulants, various experimental methods have been brought into use, but these all fall into the two main categories of water and soil cultures, with the exception of a few sand cultures which hold a kind of intermediate position, combining certain characteristics of each of the main groups. The conditions of plant life appertaining to soil and water cultures are totally different, so different that it is impossible to assume tha

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II. Details of Methods.

Many details of the sand and soil culture methods have been published by various investigators, e.g. Hiltner gives accounts of sand cultures, while the various publications issued from Rothamsted deal largely with the soil experiments. As this is the case, and as all crucial experiments have always been and must always be done in water cultures, it is only necessary to give here full details of these. The great essential for success in water culture work is strict attention to detail . Cleanline

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I. Presence of Copper in Plants.

Copper has been recognised as a normal constituent of certain plants for at least a century, so much so that in 1816 Meissner brought out a paper dealing solely with the copper content of various plant ashes. The ash of Cardamomum minus , of the root of Curcuma longa , and of “ Paradieskörner [3] ,” amongst others, were tested and all yielded copper in very small quantity. Meissner was led to conclude that copper is widespread in the vegetable kingdom, but that it exists in such minute traces th

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II. Effect of Copper on the Growth of Higher Plants.

The method of water cultures has been largely applied to determine the relation of copper compounds to plants. Twenty years ago (1893) Otto discovered the extreme sensitiveness of plants to this poison when grown under such conditions, as he found that growth was very soon checked in ordinary distilled water which on analysis proved to contain minute traces of copper. Controls grown in tap water gave far better plants, but this superiority was attributed partly to the minute traces of mineral sa

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III. Effect of Copper on Certain of the Lower Plants.

On turning to the lower plants, especially to some species of fungi, one notices a striking contrast in their behaviour to that of the higher plants. Some species of fungi have the power of living and flourishing in the presence of relatively large quantities of copper compounds, or even of copper or bronze in the solid state. Dubois (1890) found that concentrated solutions of copper sulphate, neutralised by ammonia, which were used for the immersion of gelatine plates used in photography, showe

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Conclusion.

Altogether, after looking at the question from many points of view, one is forced to the conclusion that under most typical circumstances copper compounds act as poisons to the higher plants, and that it is only under particular and peculiar conditions and in very great dilutions that any stimulative action on their part can be clearly demonstrated....

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I. Presence of Zinc in Plants.

The presence of zinc in the ash of certain plants has been recognised for many years, especially in so far as the vegetation of soils containing much zinc is concerned. Risse , before 1865, stated that most plants when grown on such soils prove to contain greater or less quantities of zinc oxide. He states that the soil at Altenberg, near Aachen, is very rich in zinc, which rises as high as 20% in places. The flora of the soil is very diversified and zinc has been determined qualitatively in mos

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II. Effect of Zinc on the Growth of Higher Plants.

In comparison with copper little work has been done with regard to the action of soluble zinc salts alone on higher plants when grown in water cultures. Freytag (1868) stated that zinc salts must be very dilute if the plants are not to be harmed, and that for zinc sulphate the concentrations must not be more than 200 mg. per litre (= 1/5000). Baumann (1885) carried out further experiments and concluded that zinc salts are far more toxic than Freytag suspected, 44 mg. zinc sulphate per litre [5]

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III. Effect of Zinc on Certain of the Lower Plants.

Among the fungi, one species stands out in special prominence on account of the great amount of work that has been done on it with regard to its reactions to zinc salts. Aspergillus niger = Sterigmatocystis nigra van Tgh was used as a test plant by Raulin (1869) , who evidently considered that zinc was an essential primary constituent of the food solutions of the fungi, ·07 parts zinc sulphate being added to each 1500 parts of water. In his experiments he tested (1) ordinary nutritive solution,

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Conclusion.

As matters stand at the present day, it appears that it is still uncertain whether higher plants grown in water cultures are susceptible to stimulation by zinc salts. If a stimulus does exist, it must be at exceedingly great dilutions, but further evidence is needed. In soil cultures, however, the fact of increased growth seems to be more firmly established, certain species responding to zinc salts when used as manure, though no increase has been obtained with other species. It must always be re

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I. Presence of Arsenic in Plants.

The occurrence of arsenic as an occasional constituent of plants has been recognised for many years. Chatin (1845) found that if a plant were supplied with arsenical compounds at the roots arsenic was absorbed, but that it was distributed unequally to the various tissues. The greatest accumulation of the element was in the floral receptacle and the leaves, while it was scarce in the fruits, seeds, stems, roots and petals. E. Davy (1859) commented on the presence of arsenic in plants cultivated f

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II. Effect of Arsenic on the Growth of Higher Plants.

The poisonous action of arsenic on plants has long been recognised. Chatin (1845) gave accounts of tissues poisoned by strong arsenical solutions. Nobbe, Baessler and Will (1884) carried on water culture experiments with buckwheat, oats, maize and alder, and found that arsenic was a particularly strong poison for these plants. When small quantities of arsenious acid (As 2 O 3 ) were added to the food solutions, growth was measurably hindered by a concentration of 1/1,000,000 As (reckoned as As).

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III. Effect of Arsenic Compounds on Certain of the Lower Plants.

Loew (1883) was sceptical concerning the specific toxicity of arsenic for plant protoplasm. He was convinced that arsenic and arsenious acid were poisonous to algae, not because of their specific character as arsenical compounds, but because of their acid nature, algae being peculiarly sensitive to any acid, and he maintained that these substances were not more poisonous than vinegar or citric acid. He placed various species of Spirogyra in solutions of ·2 gm. potassium arsenate per litre water

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Conclusion.

The toxic effect of arsenic upon higher plants is much more marked with arsenious acid and its compounds than with arsenic acid and its derivatives. No definite evidence of stimulation has yet been obtained with any arsenic compound, however great the dilution at which it is applied. With certain algae a stimulus may occur, and it is possible that arsenic acid is capable of replacing phosphoric acid to some extent under certain conditions. With fungi the toxic effect of great concentrations is m

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I. Presence of Boron in Plants.

The first claim to the discovery of boron in plants was put forward in 1857 by Wittstein and Apoiger , who carried out investigations on the Abyssinian Saoria (seeds of Maasa or Maessa picta , N.O. Primulaceae [12] ). In the course of analyses a crystalline mass was obtained which was found to contain chlorine, phosphoric acid, lime, and boric acid. The discovery apparently attracted little attention and for about another thirty years the matter was again allowed to sink into oblivion. Then it c

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II. Effect of Boron on the Growth of Higher Plants.

Excessive quantities of boric acid are decidedly poisonous to plants, the action being well marked in water cultures. Knop (1884) found that free boric acid was poisonous in neutral food solutions when present at the rate of ·5 gram per litre, but he was not able to detect boron in the ash of the roots of the experimental plants. Archangeli (1885) placed seedlings of maize, white lupins, Vicia sativa and Triticum vulgare in solutions of boric acid varying in concentration from 1–·05%, with contr

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III. Effect of Boron Compounds on Certain of the Lower Plants.

Our knowledge of the action of boron on the lower plants is less definite and complete than with regard to the higher plants. Morel (1892) found that boric acid acts as a strong poison to the lower fungi and similar organisms, their development being completely arrested by very weak solutions of the acid. He suggested, on this account, that boric acid might be used in the same way as copper to attack such diseases as mildew, anthracnose, &amp;c., which attack useful plants. On the other hand

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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

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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 m

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II. Effect of Manganese on the Growth of Higher Plants.

Little work seems to have been done on the action of manganese compounds in water cultures. Knop (1884) just indicated that manganese compounds had no effect on maize, but gave no details. Japanese investigators touched on the matter in the course of their extensive experiments with this element. Asō (1902) found that the greater concentrations of manganese sulphate exercised an injurious influence on barley. Even in solutions with as little as ·002% manganese sulphate (= 1/50,000 MnSO 4 ) the r

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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 Aspergillus niger , Penicillium glaucum and Botrytis cinerea . His general conclusion was that fungi may be stimulated, though it mus

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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 compounds which they supposed to be produced in the cells under the influence of light. The stimulation of the manganese compounds may be due to a supposed increase in the oxidising powers of the oxidising enzymes, so that destruction of the

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Conclusion.

Manganese exerts a toxic influence upon the higher plants, if it is presented in high concentration, but, in the absence of great excess of the manganese compounds, the poisoning effect is overshadowed by a definite stimulation. As is the case with boron, manganese stimulates some species more than others, the action on barley being more evident than that on peas. It seems probable that manganese may prove to be an element essential to the economy of plant life, even though the quantity usually

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CHAPTER VIII CONCLUSIONS

In the foregoing chapters a very limited number of plant poisons have been considered, yet there is sufficient evidence to show that even these few differ considerably in their action upon plant-life. This action is most variable, and it is impossible to foretell the effect of any substance upon vegetative growth without experiments. The degree of toxicity of the different poisons is not the same, and also one and the same poison varies in the intensity and nature of its action on different spec

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BIBLIOGRAPHY

The references are to pages on which authors are mentioned. Papers to which no page-references are appended are not dealt with in the text....

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