Pethybridge and Murphy — On Fhytophthora infestans. 577 



extent produced ; in some cases they were observed submerged in the medium. 

 But, on the whole, growth is decidedly poor, and no signs of oogonia or 

 antheridia were observed. 



(4) Growth on Potato-juice-wort Agar and Gelatine. — These media were 

 prepared similarly to the foregoing except that an amount of beer-wort 

 equivalent to the amount of potato-juice was added. 



Growth is very similar in these two media. For the first week or so the 

 mycelium develops and remains submerged ; then aerial mycelium arises 

 and a few conidia are borne. No sexual organs were observed, but iu the 

 agar medium swollen hyphae were quite abundant, which appeared as if 

 they might be the early stages of oogonia, but they were never observed to 

 develop into these bodies. The fungus remains alive in the agar medium 

 for many months. 



(5) Growth on " Salep " Agar. — Salep is a preparation made from the 

 dried roots of certain orchids. It was used by Bernard' in his work on the 

 fungi living in the roots of orchids, and subsequently by Klebahn' and 

 Himmelbaur,' for the culture of certain species of Fhytophthora. We first 

 endeavoured to make up an agar medium containing this substance in 

 accordance with the recipe given by the last-named worker, but found that 

 it would not set solid when cold. On leaving out the tartaric acid and the 

 inorganic salts, which seemed superfluous when ordinary tap-water was used, 

 a medium was obtained which set satisfactorily. 



, On this medium P. infestans makes slow and somewhat scanty growth. 

 A fair amount of aerial mycelium is developed, on which a considerable 

 abundance of conidia occurs, whilst there is also a fairly good development of 

 submerged mycelium, which ultimately permeates the whole of the medium. 

 No signs of sexual organs were observed in the cultures in this medium. 



(6) Growth on Lima Bean Agar, filtered and unfiltered. — This medium was 

 prepared in accordance with the directions given by Clinton, but instead of 

 straining finally through cheese-cloth as recommended/ we filtered through 

 Chardin's Agar filter-paper. We also used this medium without any final 

 filtering or straining. Considerable care is necessary in making the un- 

 filtered medium in order to avoid frothing up during subsequent sterilization. 

 On the unfiltered medium P. infestans grows quite luxuriantly, little less so 

 indeed than on the Quaker-Oat agar medium presently to be described. 



1 Bernard, N.— Eev. Gen. de Bot., xvi, 1904, p. 408. 



2 Klebahn, H.— " Krankheiten des Flieders," Berlin, 1909. p. 37. 



' Himmelbaur, W. — Zur Kenntnis der Phytophthoreen. Jahrb. d. Hamburg. Wiss. Anstalten, 

 28. Beibeft 3, 1910, p, 43. 



» Coun. Ag. Ex. Sta. Kep., 1907-8, p. 89S. 



