34 Scientific Proceedings^ Royal Dublin Society. 



liberated their zoospores after twenty minutes. The broad, apical, hyaline, 

 thickened portion of tlie wall became suddenly stretched and expanded to form 

 a sac-like structure, while the zoospores rushed out in mass, partially filling it. 

 Almost simultaneously the thin wall of the sac became ruptured, allowing the 

 zoospores to escape, whilst the wall itself quickly became unrecognizable. The 

 zoospores, which are typical of the genus Phytophthora, are lemon-shaped, and 

 each is provided with two cilia. After some time the zoospores came to rest, 

 rounded themselves off, and each produced a single germ tube. Individual 

 sporangia were seen to produce from four to twenty-six zoospores ; and the 

 openings at the ends of the empty sporangia averaged 9^ in breadth. 



In water a few sporangia produced a single genn-tube each, which generally 

 emanated from a point a little to one side of the hyaline apical region. In many 

 cases the germ-tube, after growing for a distance equal to tlie length of the parent 

 sporangium, developed at its extremity a second sporangium, which, in turn, 

 germinated by producing a germ-tube, and, as before, a terminal sporangium. In 

 this way short chains of sporangia, gradually diminishing in size, were very 

 frequently formed ; and all, with the exception of the terminal one, were devoid 

 of contents. 



The sexual organs. — Specimens with paragynous antheridia resemble in shape 

 similar organs figured from time to time for species of the Cactorum group. The 

 oogonia are pear-shaped, and arise as terminal swellings on rather short lateral 

 hyphae. The wall of the oogonium is thin compared with that of the oospore, but 

 considei'ably thicker than that of the liypha on which it is borne. The average 

 diameter of oogonia of this type from pure cultures of the fungus on artificial 

 media was found to be 28^. 



Tlie antheridia are small, irregularly shaped terminal swellings on short 

 hyphao, which spring from the parent oogonial hypha or from a neighbouring one. 

 Antheridia were occasionally observed with one or more short, finger-like, hyphal 

 outgrowths, which gave them a false appearance of being intercalary in origin. 



In the early stages of sexual reproduction an antheridium and a developing 

 oogonium meet ; the former becomes firmly attached to tlie wall of the latter at 

 any point on its surface, but perhaps most frecjueutly somewhere in the region of 

 the oogonial stalk. During fertilization only a portion of the contents of the 

 antheridium passes into the oosphere. 



The oospore, which partially or almost completely fills the oogonium, is 

 generally hyaline, spherical, thick-walled, and filled with protoplasmic contents, in 

 which are to be seen a large central oil-drop and a smaller highly refractive body. 

 Oospores from sexual organs of this type were found to average 25 '4^ in diameter, 

 and their walls varied from I'S/x to 2/^ in thickness. 



The sexual organs of the second type develop in a similar manner to that described 

 for the first time in P. erythroseptica.^ The oogonial incept grows through the 

 antheridium, and on emergence swells rapidly. The protoplasmic contents 

 gradually contract to form an oosphere, and, after fertilization, an oospore. The 

 average diameters of oogonia and oospores from sexual organs of this type were 

 found to be 27'3|U and 25fi respectively, and the walls of the oospores varied from 

 l"5;u to 2^ in thickness. 



From the characters described, and as a result of the cultural studies which 

 will be dealt with in the following section of this paper, the fungus was ultimately 

 recognized as being identical with FhytophtJwra Syringae Klebahn. 



' Sci. Proc. Roy. Dublin Soc, xiii(N.S.), No. 35, 1913, p. 529. 



