20 



KNOWLEDGE. 



[Januaby 1, 1900. 



deposited, consisting of jsarticles of a size separately 

 perceptible to the unaided vision, but on trying to seize 

 these particles between the finger they crumbled to an 

 extremely fine powder and were exceedingly soft to the 

 touch, and not in any way gritty, as would be expected 

 if of an inorganic mineral or metallic nature. 



On submitting this black dust to examination under 

 the microscope, and using a high jJower, it became 

 apjjarent that microscopic organisms were present. The 

 spores, of a dingy brown colour, were mainly elliptical 

 in form, though some were circular and some of an 

 irregular pentagonal figure ; where not crushed apart 

 they were lying in heaps, or swarm-spores in close con- 

 tact like clusters of bramble berries ; there was 

 occasionally to be seen a piece of, as it were, filamentous 

 mycelium, from which the clusters or groups of sessile 

 spores had been probably detached; the marginal 

 border of these cells was dark, while the centre position 

 was fairly permeable to the transmitted light, and some 

 few seemed to possess a tiny dark nucleus ; their 

 average size was about the 1/12,500 of an inch, though 

 many were much smaller and some few larger. On 

 examination as an opaque object they reflected a bright 

 yellow light in contrast to the dark background, but 

 were not at all affected by polarised light. It will be 

 seen that in this plate many of the elliptical sporules 

 are arranged in catinaries, with their small ends abut- 

 ting in a line with their conjugate axes, while some of 

 these elongated members appear, on minute inspection, 

 to consist of two circular sporules in close contact with 

 a more or less defined septum between the individual 

 cells. 



Again, many of these spores, more especially those of 

 elongated form, appear to be germinating by emitting 

 a thin filament, generally, though not in all cases, from 

 one of the narrow ends, this filament is appaiently in 

 some instances holding two or more in conjugation, 

 though when attached to a single cell it meiely re- 

 sembles a flagellum. 



These aerial fungi may probably have belonged to 

 the genus Rcestitia or ^cidium, both of which genera 

 are known to exist in the Cape, producing in the earlier 

 stage blight in the plants they infest, and subsequently 

 smut, mildew, or rust in the wheat and barley. 



The inky appearance of the water, both of August, 

 1888, and of August, 1899, soon cleared after it had 

 stood for a ti'ne in the vessel into which it had drained, 

 and but a comparatively small amount of sediment was 

 deposited, much less indeed than might have been ex- 

 pected, judging from the very sable tint which the fluid 

 wore upon its descent from the clouds. This black 

 water was noticed after the rainfall of the 6th August, 

 1899, in all water receptacles throughout Grahamstowu, 

 but I have not heard of its being detected in the sur- 

 rounding district. 



Such rainfalls are not without precedent in other 

 countries. Professor Barker, in April, 1849, reported 

 to the Royal Dublin Society two observations on a 

 shower of black rain that had fallen around Carlow and 

 Kilkenny and extended over an area of some 400 

 square miles. It is described as being uniformly black 

 at the time it fell, resembling ordinary writing ink, 

 but that it soon cleared after standing, and a black 

 sediment was deposited, and that the gardeners and 

 shepherds had had their clothes blackened when work- 

 ing afterwards in the clover and the fields. No 

 microscopic examination, however, seems to have been 

 made. 



Mary bomerville, in her classic work on Physical 



Geography, says — " Rain dust has been most wonder- 

 fully the means of proving that the trade winds, after 

 meeting at the Equator, cross and continue their course 

 as upper currents. Brick-red dust has frequently fallen 

 in large quantities on ships in the Atlantic, especially 

 about the Cajje cle Verd Islands, but specimens having 

 been examined by Professor Ehrenberg from the Cape 

 de Verd Islands, fi'om Malta, Genoa, Lyons, and the 

 Tyrol, he found that they all consisted of infusoria 

 and organisms whose habitat is South America." " There 

 is every reason to suppose that the dust collected by 

 Mr. Rutland in 1839, nearly midway between the 

 African and American continents, between the 10th 

 and 14th degrees of north latitude, consisted of Ameri- 

 can infusoria, " and the same authoress, writing of the 

 ubiquitous infusoria, says that Professor Ehrenberg had 



Elliptical Sporulea (magnified) in black rain. 



found them in fog, rain, and snow, and in the minute 

 dust that sometimes falls on the ocean. 



Mr. M. C. Cooke, in his work on Fungi, states that 

 recent examinations of the common atmosphere prove 

 the large quantity of spores that are continually sus- 

 pended, and, generally, in considerable numbers. The 

 majority of the cells were proved to be living and ready 

 to undergo development. A suitable pabulum being 

 exposed it was soon converted into a forest of fungoid 

 vegetation. It has been held that the atmosphere is 

 often highly charged with fungi spores. The experi- 

 ments conducted in India have been convincing on this 

 point (" Microscopic Examination of the Air," from the 

 ninth Annual Report of the Sanitary Commissioners, 

 Calcutta, 1872). 



Many of these aerial fungi have been known to attack 

 insects and use them as a basis for their parasitical 

 growth ; even the common housefly is a prey to a 

 mouldy fungus called Sparendonema Muscae, as may 

 be witnessed at certain seasons when our domestic com- 

 panion is seen to take up his last resting place on our 

 window panes surrounded with a white mouldy shroud. 



That terrible pest, the locust, is also known to fur- 

 nish a favourable medium for the cultivation of a 

 fungoid vegetation, and valuable work is now being 

 done in the Cape Colony by artificially sowing and 



