Midland Naturalist/Volume 01/The Chlorophyll-Body and Its Relation to Starch

by William Hinds

The Chlorophyll-Body and Its Relation to Starch.

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By William Hinds, Esq., M.D., Etc., Etc.,

Professor of Botany, Queen's College, Birmingham.

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ln the year 1865 I read a paper to the British Association for the Advancement of Science, an abstract of which was printed in their Transactions, to show the relation which existed between the chlorophyll-body and the starch granule. At the present time the views of some of the most eminent botanists of Germany appear to me to be, to a certain extent, approaching to the conclusions to which I have referred. What these conclusions are it is my purpose to show.

If we refer to the great English botanists of twenty years ago, we shall find them describing chlorophyll as a "vital secretion" sui generis or independent body.

One of our great authors of that period, who wrote on this subject, thus expresses himself in his Introduction to Botany^[1]:—"Chlorophyll is a 'vital secretion', and comprises 'coloured granules' of a 'spheroidal and irregular figure.' They 'consist of a semifluid, gelatinous substance, which seems to be a coagulum of the fluid contents of the cells.'"

Nägeli states that the parent cells of chlorophyll "are only half the size of starch," and that "they occur in company with starch grains."

In 1851 Dr. J. S. Quekett delivered, at the Royal College of Surgeons of England, a course of lectures on Histology, and on the subject of chlorophyll occurs the following:—"The green colour, so universally present in plants, is due to a more or less solid material contained in cells, and termed chlorophylls, or green vegetable wax." it consists of minute spherical or oval particles.

Dr. J. H. Balfour, in his Manual of Botany, 1860, page 11, states that "Chlorophylle, or the green colouring matter of plants, floats in the fluid of calls, accompanied by starch grains, it differs from starch in being confined to the superficial parenchyma, and in being principally associated with the phenomena of active vegetable life. It has a granular form, is soluble in alcohol, appears to be analogous to wax in its composition, and is developed under the agency of light."

These quotations will serve to illustrate the confusion which existed formerly, and which even new exists In many minds as to the relation which the two bodies bear to each other.

In the paper to which I have alluded, I endeavoured to show, contrary to the the received view, that starch granules and chlorophyll bodies were really the same bodies, chlorophyll granules being merely and essentially starch granules pigmented, or coloured, on some part or parts of their surface, of a green colour, by the action of light; that it was a chemical product rather than a vital secretion, or not in a fuller sense than starch was; and that, if the starch granule were not a living entity, as is the protoplasm, whence and by which it is produced, neither was the so-called chlorophyll granule, inasmuch as the colour could be produced by light without growth, or without any indication whatever of vital action. As proof of this I exhibited then, as I have over and over again subsequently, potato tubers in which chlorisation or pigmentation had occurred, or a coating of green given to the surface of the peripheral starch granules, wherever exposed to light, and a certain temperature. This light need not be the sun's direct rays, but it must be accompanied with a certain temperature in order that the chemical process shall take place. This may be easily proved. Clean potato tubers can be placed on a table, and be exposed to the direct rays of the sun, in a room the temperature of which does not exceed 40° to 45° Fah., and, if examined in a week or more, it will be found that no chemical, or no appreciable chemical change has taken place, and no pigmentation or chlorisation has been effected. Repeat this experiment in a room with a temperature of 62° Fah., and in a week the surface exposed to light will have been densely chlorized, and without direct sun-light. Extend the exposure during a few more days, and the effect will be more intense. If, now, a small portion of the substance of this green peripheral matter be scraped off and mounted in water and examined by the microscope, it will be seen that in the short space of a few days the starch granules will have been converted into what are termed chlorophyll bodies or grannies; but in reality showing, inferentially, that there is no such substance at all as a chlorophyll granule as distinct from the starch grain. It may be added that, if exposed to light and a proper temperature, granules of starch are pigmented or chlorized more or less, as soon as they are secreted, or take on substance, as seen in leaves and other organs primarily exposed to light. Hence, uncoloured starches are known to inhabit the parts of plants excluded from light, as pith, rhizomes, subterranean stems, and fruits protected by bracts impenetrable to light.

I quote one short passage from the article alluded to, and must further refer the reader to the report itself^[2] "During several years of close examination of vegetable tissue, the author has found the attempt to divide these two substances (starch and chlorophyll) into two distinct bodies a source of perplexity; and, after a series of experiments and investigations, he arrived at the conclusion that these two series of granules must be considered fundamentally the same, one series being merely coloured or chlorized."

I shall now quote one or two short passages from the latest German authorities, to show views more or less approximative to those expressed by me in 1865, and that the tendencies of the most recent scientific opinion are certainly in this direction,

Sachs^[3] states that with extremely few exceptions, grains of starch^[4] arise in the homogeneous solid substance of the chlorophyll bodies." They are at first visible as paints, gradually increase in size, and finally may so completely fill up the space of the chlorophyll grain that the green substance is represented only by a fine coating on the mature starch grain; even this costing may, under certain circumstances, disappear.”

The history in brief of the chlorophyll body, and, allowing for variations, the result of varying conditions and circumstances, would seem to be that the starch granule is first separated from the protoplasm by the ordinary vital processes; and then, according to conditions and circumstances, either becomes pigmented and assumes the condition of chlorophyll, or else remains, as it does usually when excluded from light, an unpigmented granular body, and, growing by intussusception into the perfect, enveloped starch grain, with its ordinary physical characters of hilium and concentric markings, and having in this state its known and recognised chemical characteristics. This view receives some confirmation from the following passage from Rosanoff.^[5] "The formation of the grains of the chlorophyll is not always contemporaneous with that of its colouring matter; they may be at first colourless, (as in Vancheria and Bryopsis, according to Hofmeister.) or yellow (in the case of leaves of Monocotyledons or Dicotyledons imperfectly exposed to light or in the process of development.) and may afterwards became green."

Of course it must not be assumed by any means that no pigmented red, (Rhodospermeæ, &c.,) green, or yellow matter occurs except in the form of regular granules, for amylaceous products are known and acknowledged to be often amorphous. The acknowledged chlorophyll pigmented matters and particles too are also known to occur sometimes in "bands, stars, or irregular masses." In fact there is no limit to this informality, variation, or irregularity: moreover. light itself can be dispensed with in some cases. In Angiosperms light is understood to be essential to pigmentation or chlorisation, but fern-leaves and the cotyledons of Gymnasperms will become pigmented without light.

The conclusions which I first made known in 1866, and which I may here partly reproduce, were that the almost universal green of nature Is essentially amylaceous, and can, therefore, supply fuel, at least in the matter of food, to animals. Though partly decolourised in dried grass, the same amylaceous principle is yet present. The nutritive properties of hay, which can of itself support animal life, can scarcely depend on the cellular tissue alone, and certainly not exclusively on the small proportion of nitrogen contained, nor on the fruits which, in the minor grasses, are insignificant. On the other hand, amylaceous matters are known to be intensely nutritive, as affording one main element of animal food, and not only so, but those parts of plants in which this proximate principle is concentrated are nutritive in proportion to the amount of that concentration.

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1. Lindley, fourth edition, page 138.
2. Report of British Association, 1866, page 81.
3. Julius Sachs, 1875 translation, page 46.
4. The italics are my own.
5. See translation Sachs, page 49.