132 Scientific Proceedings, Roijal Dublin Society. 



illustrations of the warty excrescences on the haulms at or near the collar. 

 Hence it may be concluded tliat there is no part of the potato-plant not 

 liable to injury by the disease. This being the case, it follows that no 

 part of the plant should be left undestroyed in attempts to eradicate the 

 disease from an aifected centre. It is known that diseased tubers leave 

 spores in the ground, and the diseased shoots no doubt do the same. 

 A diseased tuber is readily recognizable by the coral- or brain-like wart, 

 tumour, or carbuncle on it at one or more points, but especially at the 

 toe or crown end. Tlie wart is a wrinkled proliferation or corrugation of the 

 flesh of the tuber (PI. IX., fig. 2), due to excessive cell-division caused by the 

 stimulating presence of tlie fungal parasite. It is apparently an attempt on 

 the part of the host to rid itself of the enemy. Microscopic examination of 

 one of the convolutions of the wart sliows the abundance of the resting spores 

 of the fungus {Chrysojihlydis eiidobiofica, Schilb.), (PI. IX., fig. 3). To the 

 naked eye the first signs of attack of a tuber are observable in the abnormal 

 appearance or malformation of a sprouting " eye." The grey surface of 

 tlie swollen eye is dotted over with golden-yellow rings, as seen with a 

 pocket lens. The microscope shows that these rings are optical sections of 

 the walls of the resting spores, Wlien ripe these walls become dark-brown, 

 and the whole wart then looks more or less black, giving the term of " Black 

 Scab," or, better, " Black Wart," to the disease. It is unfortunate that 

 Schilberszky's (5) first and only account of the trouble in 1896, good as it is, 

 is brief, incomplete, and unillustrated. His reference to tlie crater-like 

 excavations of the potato flesh, arising in the later stages of the disease, 

 suggests that the black scab attack he had to deal with was complicated 

 by some other disease such as the deep form of Spongospora scab. Further, 

 except for the knowledge due to Potter, that the trouble, as would be expected, 

 is perpetuated by tlie resting spores, his account was not added to until 

 November, 1908, when I was able to anaouuce in Nature tliat I had 

 succeeded in making the recalcitrant resting-spores germinate. 



Chrysoplilyctis is a member of the Ciiyti-idiacese, a low group of fungi 

 having many points of affinity with the Slime fungi or Myxomycetes, and 

 being, in the opinion of some botanists, the originating group of fungi in 

 general. They are classified partly by the character of their plant- or 

 vegetative body, partly by their mode of reproduction. In the lowest forms 

 the plant-body is a naked plasmodium, and propagation is mostly vegetative : 

 in the highest there are hyphse, suggestive of a mycelium ; and reproduction 

 is sexual as well as vegetative. Ghrysophlyctis is a member of the lowest 

 group, tlie Olpidiacese. Its plasmodium is distinguishable in the host-cell 

 by being denser, homogeneous, and finely granular (PI. XL, fig. 1). It may 



