[Read before the Philosophical Institute of Canterbury, 2nd July, 1874.]

At the April meeting of the Society, a short paper, by Dr. Berggren, of the University of Lund, on the colouration of wool by Hœmatococcus sanguineus, was read. ^* A specimen was shown beneath the microscope exhibiting the dried and deformed cells of the alga nearly colourless, the fibres of wool being tinted of a pinkish hue. I have thought that some observations of my own on the colouring matter of Hœmatococcus may be worth recording in connection with Dr. Berggren's paper.

The alga consists of a diffuse formless frond found in damp places, beneath the drip of the eaves of houses, and such like. It has a dull brownish red or maroon tint, and very closely resembles a patch of half-dried blood; this resemblance is embodied in the various names—Hœmatococcus sanguineus, Palmella cruenta, and the popular name, gory dew; when quite dry the colour changes to a pinky lilac or peach colour. The frond consists of numberless discrete spherical cells embedded in a structureless matrix; the cells have beneath the microscope a pale orange red tint, the matrix being colourless.

Water, whether cold or at a boiling temperature, appears to have no action upon the colouring matter. Solution of ammonia, or other alkali, immediately changes the colour of the cells to a bright olive green.

If the frond be boiled in alcohol the spirit acquires a deep green tint, exhibiting the characteristic absorption spectrum of chlorophyll—a sharply defined black band in the extreme red.

Glycerine extracts at ordinary temperatures a colouring matter having definite characteristics. The solution of this principle in glycerine is dichroic, having by transmitted light a very beautiful carmine tint, in fact the hue is scarcely distinguishable from a very dilute ammoniacal solution of carmine. By reflected light, however, there is a very remarkable difference, for, whereas the carmine solution appears unchanged, the solution of the colouring principle of the Hœmatococcus exhibits a luminous orange cloudiness; by artificial light this is dingy yellow.

The colouring matter gives a definite absorption spectrum, consisting of a broad band commencing with a well-defined dark edge a short distance nearer the blue than the sodium line D, or about the centre of the fourth black band of Beale's absorption scale, and shades off gradually to E, where it loses itself. The spectrum may be advantageously compared with that of the solution of carmine, which, with an almost exactly similar tint, gives however a totally different spectrum, consisting of three not very well-defined bands.