42 



INJURIOUS INSECTS AND FUNGI. 



[June 1896. 



which slightly raised the embrowned epidermis. These being 

 highly magnified were seen to be composed of one or two thickly 

 tufted mycelia of mucedines (moulds). M. Roze did not recog- 

 nise Oospova scabies, Thaxter, in these forms, but considered that 

 they differed in the various excrescences examined. Under 

 these growing mycelia the cellular tissue of the first layer of 

 the parenchyma was to a great extent softened, and one or 

 two species of bacteria, more of less mobile, were observed. 

 These results corresponded fairly in all cases with those obtained 

 by American observers, and showed that these mucedines and 

 bacteria together produce by their development the future small 

 pustular cavities made by this disorder. 



But M. Roze further discovered, in examining with a magnify- 

 ing glass the surface of the Marjolin tubers thus attacked, that 

 the epidermis, or thin upper layer of skin, was covered with 

 smaller spots of a paler brown, at first pointed in shape, and 

 afterwards gradually developed into the small warty growths 

 which had been previously observed. Under the microscope 

 these very small brownish spots appeared to be formed of the 

 cellular tissue of the skin, more or less decaying, and having 

 within them a small number of extremely small rod-cells of a 

 micrococcus which could not be easily distinguished from the 

 normal constituents. These were best observed in the trans- 

 parent mucus, which adhered to the broken down walls of the 

 cellular tissue. Seen under very high powers and treated with 

 methylene blue solution, this micrococcus appeared to be nearly 

 spherical in form, and of a diameter of about the five-hundredth 

 part of a millimetre. It was also present in other dead cellular 

 tissue, and occasionally among the mycelia of mucedines which 

 pervaded the dead tissue. 



It was remarked also that the epidermis pushed up by the 

 warty excrescences always showed the cellular tissue, em- 

 browned and killed by the micrococcus. In consequence of this 

 M. Roze was led to consider that the micrococcus was the first 

 cause of this disorder, by, as it were, facilitating the introduc- 

 tion of other parasites which take advantage of the favourable 

 substratum it has prepared for them. He believes that the first 

 penetration of the epidermis of the tuber is a special faculty of 

 this new micrococcus, and that it thrives only upon the 

 epidermis (epiderme), or the skin (peau), whose cellular tissue 

 it destroys. M. Roze names it Micrococcus pellucidus, and 

 observes that it is able to exist not only on potato tubers out of 

 the ground, but also in the ground. 



Although Drs. Thaxter and Bolley succeeded in inoculating 

 sound potato tubers with their Oospora scabies and their 

 bacterium — and this might be considered as a proof that these 

 parasites were the primary cause of the malady — M. Roze holds 

 that this is explained by the results of an experiment he made 

 by inoculating potato tubers of the variety known as Victor, 

 with spores of Fusisporium solani. The tubers were not at 



