160 ROYAL SOCIETY OF CANADA 



stage of the preparation, but best, perhaps, after adding the sugar. 

 The addition of this chemical makes the medium lighter in colour and 

 strongly acid to litmus and to phenolphthalein. 



A living culture of Ps. radicicola will usually grow well in one 

 or all of the following three liquid media, the preparation of which 

 can be varied as before indicated. Such media can be sterilized in 

 flasks and stored indefinitely. 



To 1,000 c.c. of distilled water add 15 grams of wood ashes, heat 

 in flowing steam, boil a minute and filter. 



To 400 c.c. of the filtrate add 4 grams maltose. 



To 200 c.c. of the filtrate add 100 c.c. distilled water and 3 grams 

 maltose. 



Heat these three solutions half an hour in fiowing steam and boil 

 a moment over the flame, or else heat for 10 minutes at 10 pounds 

 steam pressure in the autoclave. Filter clear, tube each lot separately, 

 and sterilize in flowing steam or in autoclave at 10 pounds steam pres- 

 sure for 10 to 20 minutes. 



Sugar-ash-agar for Ps. radicicola. — The materials and methods of 

 preparation are, in general, the same as for the liquid media except 

 that aga.r is used in addition. The sugar may vary from 4 to 20 parts 

 per 1,000, the ash from to 50 parts per 1,000, the agar from 7.5 

 to 15 parts per 1,000, and the acid potassium phosphate may be omitted 

 or used, from 5 to 10 parts per 1,000. It is best to fllter the ashes 

 from the water before adding the remaining ingredients and to dissolve 

 the agar in the ash water before adding the maltose. If acid phos- 

 phate is added at all it should be ,only when 10 parts or more of ashes 

 per 1,000 are used, and then after adding the maltose. In making up 

 a series of agar media the several parts can be prepared separately in 

 such proportions that, on mixing determined volumes and adding vari- 

 able quantities of water, media will result having the desired composi- 

 tions. 



The three media of the following compositions were found favour- 

 able: — Water. 100 parts; maltose, 1 part; agar, 1 part; and the soluble 

 portion of ashes, 1 part, 1.5 parts and 2.5 parts respectively, prepared 

 as below. 



Solution " A '*' — Water 100 parts, maltose 2 parts, agar 2 parts, 

 heat together until dissolved. 



Solution " B " — ^^^^ater 100 parts, ashes 5 parts, boil and fllter. 

 Solution " A." Solution " B." Water. 



100 40 60 



100 60 40 



100 100 



