22 Scientific Proceedings^ Royal Dublin Society. 



in which bacteria were plentiful, but no Phytophthora was present ; and all 

 efforts to discover this fungus on either of these two plants during the period 

 named met with absolutely negative results. This part of the experiment, 

 therefore, confirms the previous part, the results being in both cages the 

 production from diseased sets of plants entirely free from Photophthora 

 under conditions extremely favourable to the fungus and withal adverse to 

 the plant. 



The result is the exact opposite to that obtained by Massee, who obtained 

 diseased plants from diseased sets in five cases out of six ; but, as pointed out 

 above, in the absence of controls, it is impossible to assume with any degree 

 of certainty that these plants became affected directly through tlie tubers. 

 On the other hand, the result. of my experiment is in agreement with those 

 of many previous workers which are in the main to the effect that tubers 

 affected with Phytophthora produce healthy plants ; and tlie idea that the 

 recurrence of the potato-disease year after year is due to the migration 

 of dormant Phytophthora mycelium, in or into apparently healtliy plants 

 during unfavourable seasons of weather in the summer, can only be regarded 

 as a theory with no evidence to support it. 



During the summer the question of the production of healthy or diseased 

 plants from diseased tubers was further tested at the Temporary Station for 

 the Investigation of Plant Diseases at Clifden, Co. Galway. A single ridge 

 of reclaimed bog-soil, occupying an area of about one square perch, was 

 planted with 132 uncut " champion " tubers, attacked by Phytophthora, 

 on April 12th. Only fifty-three of these produced plants; the remaining 

 seventy-nine rotted in the ground without doing so. The fifty-three plants 

 were not quite so robust as neighbouring ones grown from healthy tubers; 

 but they showed absolutely no signs of Phytophthora until July loth. On 

 this date the blight was found as isolated spots here and there on the leaflets 

 in the ordinary fashion, indicating an attack from spores borne from 

 neighbouring plots, some of which were attacked with it three weeks earlier. 

 It seems quite impossible to believe that these spots of blight, in many cases 

 on isolated outstanding leaflets, could have arisen from internal mycelium, 

 while the remaining portions of the plants, including the stalks, were quite 

 healthy. How could Phytophthora, if present internally, have succeeded in 

 carrying on an existence for over three months without exhibiting some 

 signs of its presence? Even if it remained alive in the tubers all this time, 

 which is to say the least most unlikely, how could it possibly have grown up 

 through the stalks and out to the leaflets without leaving some impression of 

 its strongly parasitic and destructive characters on the tissues through which 

 it progressed ? Comparisons have been made between the supposedly 



