Johnson — Further Observations on Powdery Potato-Scab. 173 



Lagerheira did not see any early stages of spore- formation, but presumes 

 tliat, according to their mature structure, "neighbouring hyphse develop upon 

 the pseud-parenchyma, and divide up into small cells, which cling firmly to 

 and partly surround the sporogenous hyphse." The spores could not be 

 made to germinate, and Lagerlieim's statement is not illustrated, but the 

 reconciliation of his observations with those of Brunchorst is to be found 

 possibly in the account I have given of the smut-like organism. It is 

 possible, judging from some preparations I have, that a third organism may 

 produce yet another form of powdery scab. Lagerheim concludes that his 

 fungus is the same as that called Sponfjospora Solani by Brunchorst, and that 

 it has been long known and ilescribed by various authors as JEri/sibe sub- 

 terranea Wallroth. "Unfortunately," he says, "the publications of Wallroth, 

 Martins, and Berkeley are not accessible to me, which renders it impossible 

 for me to decide this question. If my supposition be correct, the fungus 

 sliould be called Spongospora mbterranea (Wallr.) " — a name I had decided to 

 adopt loug before my attention was called to Lagerheim's note. 



(A somewhat parallel case is mentioned by Sorauer in his Handbuch : — 

 The coral-like swellings on the roots of the alder, bog myrtle, &c., were at 

 one time described as due to a filamentous fungus SMnzia Alni. Moller then 

 attributed them to a plasmodium to which he referred the Schinzia. Woronin 

 saw the two forms existing side by side. Brunchorst, it is interesting to note, 

 next saw no signs of a plasmodium, but a filamentous fundus, which he 

 distinguished from Schiuzia as Frankm mbtiUs. Finally, Bjorkenheim 

 concludes the fungus is a filamentous one, with swollen hyplise, which form 

 bladder-like swellings, mistaken for spores by earlier observers.) 



Prevention of the Disease. 

 In 1909 I made a number of experiments by pot cultures to test the 

 possibility of preventing Spongospora scab. In all cases the soil was good 

 garden loam, and healthy seed in it gave a healthy crop. 



1. Seed-tubers of the varieties Red Skerries and Champions suffering 



from scab gave a scabby crop. 



2. Similar seed first treated for eighteen or twenty-four hours, with a 



2 per cent, solution of Bordeaux mixture, gave tubers free from scab. 



3. Such seed treated with sulphur gave a scabby crop. 



4. 1 planted healthy tubers of Sutton's Superlative, into whicli I had 



previously grafted a wedge of a scabby tuber, from which all the 

 spore-balls, as far as I could make sure, had been scraped off. The 

 tubers formed were scabby. Thus it appears that the resting 

 Plasmodium can communicate iufeotion to healthy tubers. 



SCIENT. PBGC. R.D.S., VOL. XII., NO. XVI. 2 P 



