44 Tramactions. — Zoology. 



paper (figs. 2c, 'Hd, 2e) rough representations of three different 



forms observed.! 



The economic point, however, to which I di-aw attention is 

 that, as a general rule (I might even put it more strongly), the 

 appearance of this black fungus is an indication of the presence 

 of homopterous insects ; probably, m New Zealand, of Coccidae, 

 because they are the most numerous of the order in this 

 country. Now, a great deal has been heard of late years of the 

 damages by scale-insects, and all sorts of people have written or 

 experimented about them. I find that, amongst the diseases of 

 trees, this black fungus-growth has attracted attention : but the 

 misconception to which I alluded just now is that it has been 

 considered as a separate, or primary, disease, which I do not 

 think it is. 



In Mr. Kirk's " Eeport upon the Diseases of Lemon and 

 other trees in New Zealand," the common notion is em- 

 bodied, and, under the head of " Lemon Smut, or Black Blight," 

 the writer even emphasizes it, by saying that the excreta of 

 Icerya purchasi (a scale-insect) had no share in its production, 

 and that it was of " purely vegetable origin." In answering, in 

 1885, questions by a Select Committee of the General Assembly 

 upon tree-diseases, I combatted this view, and ascribed the 

 black " smut" to fungoid growths, the result of the presence of 

 homopterous insects. I believe that Mr. Kirk has now come 

 round to this view of the question, which is, undoubtedly, the 

 right one. 



It stands to reason, then, that if a farmer, or orchard- 

 grower, or gardener, observing this black growth on his trees, 

 imagines it to be the primary cause of disease, and sets to work 

 to eradicate it without attending to the insect pests, he will be 

 simply throwing his labour away. And there is this important 

 fact to be remembered, that it is not with scale-insects as with 

 other iu sects. Coccidae are impervious to many thuags which 

 might, in other cases, be efficacious. There is a common belief 

 which, like most superstitions, it is excessively difficult to de- 

 stroy, that sulphur is an useful ingredient in what are called 

 " scaly-blight destroyers." I should not be in the least surprised 

 to find that many who hold this belief do so because they have 

 found the black fungus disappear, or lessen, after its use, for 

 sulphur is undoubtedly a remedy for fungoid blights — e.g., oidium, 

 etc. ; and probably they never thought of looking more closely 

 into the matter. All experience goes to show that sulphur, 

 unless applied in such strength as to burn up insects, fungus, 

 tree and all, is not a remedy against Coccids. Comstock, Riley, 

 Hubbard, and others agree in this : and although, in newspaper 



J Boudier (Assoc. Fran, pour I'avancement des Sc, 1884) includes the 

 European fungi developed in the honeydew of Aphis in the genus Clado- 

 sporhim (Quart. Journ. Roy. Micros. Soc, Aug. 1886, p. 597). 



