108 ON AN ACARUS ASSOCIATED WITH BANANA ; 
It is not likely that the banana mite is T. Queenslandiz*® of 
Canestrini, found with quite different habits a few years ago in 
this colony, and which, like other Detriticolee that occur at 
Brisbane also, is probably a typical ‘l'yroglyphus. 
This species of Rhizoglyphus has been observed wandering 
on the stems of the banana in question; between the chaffy 
scales which occur in these plants just above the ground; and 
on the roots. In the last situation it was met with beneath 
the epidermis, which was split transversely, at the seat of injury. 
When this epidermis was removed it was found that it had become 
detached from the subjacent tissue, which, darkened in colour, had 
either shrunk, or been gnawed, back to a level with the central 
bundle. The surface of this discoloured portion was covered with 
a meal-like substance, characteristic of the presence of mites of the 
tribe to which the banana acarus belongs. ‘The term ‘“‘ rust,” as 
applied to the diseased condition, has been assigned owing to the 
occurrence on the surface of the stem of the banana, and on the 
exposed portions of the fleshy parts of the leaves generally, of small 
purplish specs, which, by confluence, form spots, blotches, or 
clouds of the same colour. Microscopic examination reveals the 
fact that these specs surround minute punctures in the epiderm. 
To account for the presence of these coloured specs it is only 
necessary to bear in mind that every portion, perhaps, of the 
banana contains a large quantity of tannin, and even so the fruit, 
according to the analysis of Mons. Marcano and Munz (Comp. 
Rend. 88, 156-158.) Under the natural process of maturation 
this tannin in the latter position is converted into glucose and 
another substance ; but in those parts in which this resolution does 
not take place, the tannin, on exposure to the atmosphere and by 
reason of its avidity for oxygen, especially in the presence of an 
alkali, is converted into a dark purple coloured body. Hence 
the use of the juice of the banana as a marking ink. Hence also 
the occurrence of the specs, spots, or blotches of purple colour, 
according to the extent of the affections, on plants which may have 
been injured owing to the attacks of insects or through other 
causes. ‘This disease, though found on bananas, Is quite distinct, 
in the symptoms which manifest its presence from that occasioned 
by the rhabdiform worms which constitute the “ flask worm” dis- 
ease of Dr. Bancroft, or from the following maladies of fungoid 
origin :—The black felt-like spots on the leaves and the brown 
confluent ridges on the surface of the fruit, known to be caused 
* Berl. Ent. Zeitsch, 1884, p. 721, fig. 
