580 Scientific Proceedings^ Royal Duhlin Society. 



sufiBciently so as to cause the cells themselves to burst, remained distributed 

 here and there throughout the medium. These cells were about the same size 

 as the oogonia; and since their walls were also brown, it was impossible to 

 distinguish them from the oogonia without the use of the compound micro- 

 scope. Hence when looking over culture-tubes for the presence of oogonia 

 with a pocket-lens, the pre.sence of these bodies was the cause of considerable 

 inconvenience. 



Grotmd Quaker-Oats Agar. — This is the medium which has given us the 

 best results ; it is prepared as follows : — 



Thirty grams of Quaker Oats' are ground in a small hand-mill, with 

 adjustable frictional surfaces, to as fine a powder as possible. This is then 

 stirred into 500 c.c. of cold water (rain-water or soft water), and placed in the 

 inner vessel of a double saucepan, cold water being placed in the outer. The 

 saucepan is then warmed up ; and in from ten to fifteen minutes the oatmeal 

 and water form a rather thin gruel. At this stage 10 grams of strip agar, 

 cut into small pieces, are added, and the heating is continued until the latter 

 has become completely dissolved, the latter process being facilitated by 

 constant stirring. The medium thus prepared is free from lumps, and can 

 easily be poured iuto test-tubes which are then sterilized in the autoclave, 

 slanted, and allowed to cool. No water is added to make up for the small 

 quantity lost during the cooking process. If the Quaker Oats are not ground 

 fine before using, the medium will be lumpy and stiff. The annoying brown 

 cells, present in our preparations of oats, according to Clinton's method, are 

 entirely absent in this medium. 



The growth of P. infestans on this medium is similar to that on Clinton's 

 oat-juice agar, but somewhat more luxuriant. The aerial mycelium is more 

 copious, and conidia are formed in very great abundance. Conidiophores 

 which have produced ten conidia on the same hypha are not uncommon, and 

 one was observed which had borne thirteen without becoming branched. 



Oogonia were borne by the fungus on this medium in far greater abundance 

 than on Clinton's oat-juice agar. Out of seventy- seven of our earlier cultures 

 on it only eleven failed to produce any, and thirty-four of the remainder 

 produced them very abundantly. 



Antheridia have been found on this medium as well as oogonia, but up to 

 the present in only three cultures of one and the same series, although, in all 

 probability, they will contiuue to develop more abundantly as time 

 progresses. 



' Quaker Oats is a proprietary article of food made in Canada by the Quaker Oats Company for 

 Quaker Oats, Limited, London. It appears to consist of partially cooked, crushed oat caryopses, 

 without the pales. 



