496 Scientific Proceedings, Royal Dublin Society. 



On resuming the work in October this examination revealed the abundant 

 presence of sexual organs in the original stock cultures, which, however, at 

 this time were dead ; and these organs were also found in a few of the inter- 

 mediate transfers, the more recent of which were still living. They were also 

 produced, but not very abundantly, in sub-cultures made subsequently ; and 

 it was found that they developed rather more readily in a hard Quaker Oat- 

 agar medium containing 12i per cent, of agar than in the one usually 

 employed, which contains only 1| per cent, of agar. 



The sexual organs are of the type first described for Phytophthora 

 erythroseptica (4) and P. infestans (8). It is, therefore, clear that the fungus 

 is a true Phytophthora. Using Murphy's (3) terminology the antheridia are 

 amphigynous and not paragynous, as in the genus Nozemia. 



The antheridium may be terminal or intercalary, and often has a short 

 hypha proceeding from it, as in P. erythroseptica, which, as Murphy has 

 suggested, may play the part of a safety-valve by relieving the pressure 

 caused by the growth of the oogonial incept when within the antheridium. 

 Pipe antheridia are variable in form and size, and their dimensions are not 

 of much import for diagnostic purposes. 



The oogonium may also be terminal, but it is more usually a lateral out- 

 growth. When ripe it is pear- or balloon-shaped. The oogonial incept having 

 penetrated the antheridium and emerged from its top swells up to form an 

 almost spherical sac in which the oospore is developed. The lower, funnel- 

 shaped base of the oogonium remains within the antheridium and becomes 

 closed at its narrow end with a cellulose plug. The rather thin wall of the 

 oogonium is at first hyaline, but becomes amber-coloured with age. The 

 average diameter of the spherical part of the oogonium is 30,u. 



Fertilization probably occurs in the manner described by Murphy (3) for 

 P. erythroseptica; and the oosphere develops into a thick-walled oospore, 

 which, when ripe, contains a large oil drop surrounded by finely granular 

 protoplasm in which a small oval highly refractive body lies which possibly 

 contains the nucleus. The wall of the oospore, at first hyaline, becomes straw- 

 coloured, and averages about 3/u in thickness, while the diameter of the spore 

 averages 25/i. The germination of the oospores developed in pure cultures 

 has not yet been followed. The sexual organs are illustrated in figs 3, 4, and 

 5, Plate XLV, and fig. 11, Plate XLVII. 



VI. — PRECOGNITION OF THE FUNGUS AS A NEW SPECIES. 



The peculiar morphology and mode of development of the sexual organs 

 first discovered in Phytophthora erythroseptica, P. infestans, P. Phaseoli, and 

 surmised to occur in P. omnivora var, Arecae, led to the suggestion (4), (6) 



