20 Scientific Proceedings, Royal Dublin Society. 



diseased sets in tliem, together with the twelve pots of unsterilized soil con- 

 taining six Iiealtliy and six diseased sets, were placed at the same time in a cool 

 greenliouse witli no artificial lieat and with an exceptionally dry atmospliere. 



As regards tlie tliree liealtliy (control) and tlie three diseased sets in the 

 warm liouse, two of tlie latter produced overground stalks after twelve days, 

 while tlie tliird one, although left for some considerable time longer, did not 

 do so, and was found to liave completely rotted away in the soil. A week 

 later overground shoots were also produced from tlie tliree liealtliy sets, and 

 tliese grew into large, perfectly' liealtliy specimens, whicJi were of course 

 somewhat etiolated or "drawn," but which up to tlie end of the experiment 

 never showed the sliglitest signs of Pliytophtliora or any otlier fungus on 

 them. The plants from tlie two diseased sets also developed well, but in a 

 slightlj'' less robust fashion. One of them remained in every respect perfectly 

 liealthy and absolutely free from any form of disease whatever until the end 

 of the experiment. Tlie other one had but two stalks, one of which was very 

 weakly from the start, but not owing to the presence of Pliytoj^htliora in it. 

 After a short time one or two of the leaflets on fjiis feeble stalk became 

 blackened at tlieir very tijDS. These leaflets were kept under close observa- 

 tion with the microscope, but only Botrytis developed on them, not Pliytoph- 

 tliora. By degrees this feeble shoot gradually succumbed from above 

 downwards. It was kept under close and constant observation ; and when 

 nearly dead it was removed and subjected to further microscopic observation 

 and incubation, but not tlie slightest trace of Pliytophtliora was found on it 

 at any time. The other stalk of this plant grew well, and remained entirely 

 free from disease of any kind until the end of tlie experiment. Hence this 

 part of the experiment resulted in the production of two plants absolutely 

 free from Pliytophtliora from two diseased sets, placed under conditions 

 extremely favourable to the development of this fungus. 



Of the eighteen sets (nine diseased and nine healthy) in the pots in the 

 cool greenhouse, most of the diseased ones produced overground shoots earlier 

 than the healthy ones; but out of the nine diseased sets, three produced no 

 plants, and were found to have completely rotted in the soil. AH the nine 

 healthy sets produced healthy plants. The plants developing from the 

 diseased sets were here, as in the warm house also, somewhat less robust 

 than those from the liealthy ones, and one in particular (No. 15) produced a 

 shoot only 2 or 3 inclies high which quickly became diseased from below 

 upwards, and soon died. Doubtless the mycelium had entered tlie shoot 

 from the parent set. Tliis plant was removed as soon as possible for fear 

 of its causing the infection of the neighbouring ones by "spores." Up to 

 April 27th all the plants in tlie cool liouse, with the above exception, had 



