36 Scientific Proceedings^ Royal Duhlin Societij. 



Again, some of Ihe figures illustrating de Bary's' own account of P. omnivora, 

 especially figs. 25, 26, and 27 on Taf. Ill (concerning which it is stated that the 

 point of origin of the oogonium was hidden by the antheridium), are suggestive, at 

 least, of cases where the antheridia may have been amphigynous. 



llosenbaum,- in dealing with P. Cactorum isolated from diseased Ginseng, 

 figures the sexual organs with paragynous antheridia only ; but he states that " in 

 some cases the stalks bearing the antheridium and oogonium are on the same side, 

 and the antheridium then falls on the oogonial stalk. Under the microscope, such 

 a condition may present the appearance that the oogonium has grown through the 

 antheridium." It seems quite likely that the "appearance" in the cases noted 

 may, indeed, also have been the reality. 



In view of tlie uncertainty which appeared to exist in the matter, it was 

 considered desirable to make renewed studies of P. Cactorum and P.Fac/i, and to 

 compare the fungus isolated from the Irish rotted apples with these species, and 

 also with others isolated from decayed apples and pears in other countries, so far 

 as it was possible to obtain them. Later on it was found necessary to re-examine 

 P. Syringae. 



As soon as it had been established clearly that the two types of sexual organs 

 found in the Irish apples were produced by one and the same fungus, the attention 

 of mycologists was called to the matter in a letter to " Nature,"' and an appeal 

 was made for cultures of species of Phytophthora from other workers. 



From Dr. W. F. Bewley, of the Experimental and Eesearch Station, Cheshuut, 

 Herts, a culture was received provisionally regarded by him as one of P. Cactorum. 

 The fungus had been isolated from a rotten apple purchased in Chesluint. 

 Professor H. PI. Whetzel was good enough to send a culture of what he regarded 

 as P. Cadorwni, isolated from a decayed apple grown in his own garden in 

 Cornell University, Ithaca, New York State, U.S.A. Dr. A. Osterwalder kindly 

 sent from the Swiss Eesearch Station for Fruit, Vine, and Garden Cultivation in 

 Wadenswil a pear affected with a Phytophthora-rot, from which what appeared tp 

 be P. Cactonmi was isolated without difficulty. Cultures of P. Cactorum arid 

 P. Fagi (stated to have been isolated by Peters from Cactus and Fagus sylvatica 

 seedlings respectively) and one of P. Syringae (originally isolated in Hamburg by 

 Klebahn from Syringa vulgaris) were obtained from the Centraalbureau voor 

 Schimmelcultures in Baarn, Holland, through the kindness of Dr. J. Westerdijk. 



Including tlie species isolated from the Irish apples, there w-ere thus seven 

 cultures of allied Phytophthoi-as, each from a different source ; and these formed 

 the basis of a series of sub-cultures on various media, which were studied in 

 considerable detail. Limitations of space preclude the description in extenso of 

 this comparative cultural work, and only the most important results can be dealt 

 with here. 



In the first place, it may be stated that each of these fungi, when inoculated 

 through wounds into healthy apples and pears, was found to be capable of setting 

 up in them a characteristic form of brown rot, similar to that described in the 

 present communication. Apart from minor \'ariations, such as the number and 

 size of the tufts of hyphae protruding through the lenticels, and so on, these forms 

 of rot were indistinguishable from one another by the naked eye. 



Secondly, it was found that each of the fungi produced sexual organs of the 



iBeitr. z. Morph. u. Phys. derPilze, iv, Frankfurt a. M., 1881, p. 22. 



2 N.Y. State Coll. Agric. Cornell Univ., Bull. 363, 1915, p. 100. 



3 Vol. cvii, No. 2685, April 14th, 1921, p. 204. 



