ON WHITE RUST. 49 



cell often seated obliquely, so as to call to mind exactly the yeast 

 fungus. An examination however of the youngest individuals we 

 could find, detected extremely short moniliform threads like 

 those of some of the more minute Oidia, as 0. circinans, and it 

 is to that genus, notwithstanding some difficulties, that we think 

 the little parasite must be referred. At first we were inclined to 

 consider it a Glceosporium, especially in consequence of the waxy 

 appearance mentioned above, which does not exist in any recorded 

 Oidium, and which is due to some gelatinous element in the 

 outer coat of the spores, the absence of which renders the spores 

 of normal Oidia pulverulent, but not only was there nothing like 

 distinct pustules in some shape or other essential to Glceosporium, 

 but the moniliform growth of the spores was decisive as to the 

 impropriety of such an arrangement. Unless admission be 

 conceded into Oidium, a new genus must be framed, which we 

 are unwilling to do on the mere circumstance of the spores having 

 a little more gelatinous matter in their outer walls than is usual 

 in the genus. About the time when the parasite appeared. Dr. 

 Montagne kindly communicated to me a somewhat similar pro- 

 duction which had occurred in the South of France on walnut 

 trees, consisting like this of minute white spores, none of which 

 however exhibited any tendency to become moniliform. This he 

 has referred to the genus Gymnosporium, under the name of 

 G. leucosporum, to which genus I should gladly have assigned my 

 minute fungus, but for the Oidioid mode of growth. It may be ob- 

 served moreover that the spores of Dr. Montagne's plant strongly 

 resemble those of the Pear Fungus, measuring -g-5'0-0 of an inch 

 in length, a size which differs very little fi'om that of the Oidium. 

 There is however a circumstance connected with the little 

 parasite which requires notice. When it was first submitted to 

 Mr. Broome, he detected what appeared to be perfect asci, con- 

 taining hyaline bodies of the same shape as the spores, but 

 averaging -^-^-q of an inch in length. The question at first 

 occurred whether these had not been poured forth from the little 

 sacs so as to form a thin white stratum, but the difference of size, 

 though the form was identical, was against such a view, and the 

 discovery of the moniliform mode of increase was still more 

 decisive."' The apparent asci were no doubt individualised cells 



* The production noticed by Dr. Moutagne on walnut leaves was no leg.s 

 remarkable for the total absence of sporopliores, insomuch that, as in the 

 pear leaf, the bodies might be supposed to have been poured out from the 

 asciform cells but from their evident increase by the addition of new cells, 



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