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Art. LV.—On the Occurrence of Hæmatoccus sanguineus on the Wool of
a dead Sheep.
Plate XXIV.
[Read before the Philosophical Institute of Canterbury, 2nd April, 1874.]
That group amongst the Algæ, which was formerly included under the term Protococcus, contains several species, which by their occurrence together in enormous numbers suffuse with a characteristic colour the substance upon which they grow.
To this section of plants belongs the so-called “red snow,” which consists of simple roundish microscopic red cells, by which the ice and snow of alpine and polar regions are coloured red; another species sometimes grows in swamps and canals imparting to the water a similar hue; while to another, luxuriating in certain portions of the ocean, the Red Sea owes its name.
There are also species which form a red covering upon mosses or rocks; others again grow upon vegetable products used by man, for instance, fruit and bread—an occurrence which has given rise to remarkable errors of even historical importance as to their origin and nature.
Similar Algæ appear also occasionally upon animal bodies. Thus I found
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upon the wool of a dead sheep in the New Zealand Alps, in the neighbourhood of the West Coast road, a species which, as far as microscopic examination has hitherto shown, is Hœmatococcus sanguineus.
This plant, forming blood-red spots upon the wool, consists of globular cells, invisible to the naked eye. Viewed under the microscope, the globules exhibit a golden-yellow colour, whilst the fibres of the wool are scarlet-red. This colour without doubt is derived from the red pigment of the cells, which has been pressed out from some cause impregnating the fibres.
The portion of the wool which was not exposed directly to the light has a green appearance, and this colour is most probably of the same origin as the red.
An analogous example of the change of colours is furnished by the plant which forms the so-called “red snow” mentioned above. Whilst the contents of the cells in a certain stage of their development are purple red, they change to a green colour in another; and one of the Algæ which imparts to the surface of the water a blood-red appearance, exhibits this colour only when subjected to the direct rays of the sun; the higher the light, the more intense the colour appears. At other times the plant is green.
A specimen of wool (sent to the Canterbury Museum by Messrs. Studholme Brothers), showing a green-colour and taken from a living sheep, was shown to me by Dr. Haast, but this may be due to some infiltration of some mineral colour, although it has all the appearance of having been produced by a similar cause. It is true that all the fibres are uniformly coloured, but the Algæ originally growing amongst the wool may have been destroyed, leaving only the traces of their former existence in the fibres of the wool. It is desirable that further specimens presenting this uncommon appearance should be collected by persons having the opportunity of doing so.
Plate XXIV.—Fig. 1, Fibres of wool and Alga magnified. 2. Alga still more magnified.