NATURE'S DYE WORKS.

Shannon News, 17 June 1924, Page 4

NATURE'S DYE WORKS.

COI/GUR IN ANISIAIiS AND ’ PLANTS. PIGMENTS AND”REFRACTED EIGHT. While he thoughfully refrained -itom repeating the' old joke about e chameleon that was placed on the Scotch tartan, and also about the one that wandered on to a Persian carpet, Professor J. C. Johnson did explain to his audience at St. Andrew s . Hall, Lower Symonds Street, lust evening how that strange little animal was able to accommodate itself to almost any coloured background., The professor, who is head of the department of biology at. the Auckland University College, and was lecturing under the auspices of the Auckland Institute, gave his audience the result of some of the •most recent work in connection with the colouration of plants and annuals, and explained incidentally that there was still a great deal to be done in connection with that relat.ngw o ; animals. , . . Starting vvitk plants, he showed by means of coloured lantern slideß and experiments that the colour was due to actual pigment contained in the cell sap in the case of violets, rosea, and blue, violet, and pink flowers, and due to minute grains of pigment in cells in the case of green structures, orange, some red and yellow flowers, in the carrot, and in the tomato. With a jar of blue litmus solution) the leci tuver showed liow the pigments in plants could be changed from blue to I red by the addition of an’acid, and purple by the addition of an alkaline. •

Turning- tq the consideration of animals, Professor Johnson said there was only one’principal pigment found in them, and it was almost universal from the lowest type Up to man. It •was known as melanin, a Greek word meaning "black.'?’ Contrary to what one might think, the colouring of--ani-mals was much ic ,-i r-olid and was more mottled than it apvcarcd to the eye. At a distance the colour looked very uniform, but a close examination would show that it was verv much mottled. The melanin was found distributed very much through the animal’s structure, even to the ends of the hairs,)and the result was black, or brown where tho colouring was intermediate, and white where there was no melanin but there were air bubbles in the structure.

Explaining the remarkable manner in which the chameleon and certain frogs could harmonize with their backgrounds,. tho professor said the pigment,' melanin was normally ated in the centre of the cells, but under certain excitation from the environment of the animal the melanin was sent out to the edges of the cells, and so changed the mottling if the animal, which uiider the hew grouping as it were, harmonised with the background on which it was placed. That was one of the most interesting phases of what was known as protective colouringl. Another instance of the faculty was shown in the case of a fish ,that could harmonize with its background when it was changed from;shell sand to rocky bottom. THE COLOURING OF BIRDS.

By nleans of 'actual specimens the lecturer gave am admirable idea bf the manner in which birds gets Their wonderful colouring. The vivid yellow and black regent bii'd, for instance owed its colouration to pigment that could be extracted just as the pigment in plants l could, be extracted chemically by means of alcohol. In this connection the Professor said Nature’s colours were waterproof, but the red in the head of some brilliant* parrots would actually como out to some extent if soaked in water. He was careful to explain that the gorgeous metallic colouring seen on some birds, such as the bird of paradise, “the livelier iris that gleams upon the burnished dove,” was a purely artificial effect), and was not due to pigment at all. The light in striking the peculiar formation of the feathers struggled through was split up, and what was reflected back gave those gorgeous metallic blue, effects. That effect was seen in birds of pai’adise, in some butterflies and parakeets. Examination had failed to .find any pigment in the feathers that gave this metallic effect; the colour was due entirely to an optical effect. There was no such pigment in Nature. I The beautiful silvery effect seen on pearls and similar objects was probably due to'minute scratches , on the surface—anyhow, the effect! was entirely physical, duo to the phenomenon known as the interference with light. Incidentally the professor said that if designers only knew of the beauty of what could be seen under tii c microscope, such, for instance as parts of a butterfly's wing and'similar objects a study of the microscopo would be compulsory in art schools. The Professor showed the intimate, connetion that existed betwen light and colour and life and how the growth was modified by putting a plant under certain coloured glases, and so shutting off certain portions of the spectrum. He dealt fujlly.pn the interesting facts connected with the protective colouring of animals to enablfe them to escape their enemies, and he also fully explained the fascinating subject of the inheritance of colour and matter that had had much attention directed to it! ! since Mendel’s experiments became known. It was shown that anirnals inherited colour according to definite laws, and the facts connected with that subject were of considerable economic importance in agriculture and in other connections. In concluding a most interesting lecture the Professor referred to the artistic aspects of his subject and of the stimulus of Nature tfo art.