492 Scientific Proceedings, Royal Dublin Society. 



the fungus (presumably a Phytophthora, and possibly identical with the one 

 now being dealt with) which causes the " Black Neck " disease of Asters. 



Less commonly than by the production of zoospores the sporangium 

 develops by producing a single germ-tube, which usually arises at the distal 

 end of the sporangium (figs. 5 and 6, PL XLVIL). One very unusual case was 

 observed, however (fig. 10, PI. XLVIL), in which a single sporangium developed 

 a considerable number of germ-tubes, one of which (much shorter than any 

 of the others) proceeded from the usual place, while the others were distributed 

 at various points over the surface. The appearance suggested that partial 

 segregation into zoospore- units had occurred ; the sporangium did not, how- 

 ever, open, and the free swimming stage of the zoospores was suppressed. 

 Nevertheless, each zoospore- unit developed its own germ -tube, which grew 

 out in the manner illustrated. 



A very considerable amount of time and trouble has been spent in 

 searching for the sexual organs of the fungus in the dead tissues of the host 

 plant both when naturally infected as well as when artificially inoculated. 

 What appear to be undoubted oospores of some fungus, frequently still 

 surrounded by the remains of the oogonial wall, have occasionally been met 

 with, but in no case has an antheridium been observed. These spores are 

 somewhat smaller than those which are produced by the fungus when grown 

 in pure culture ; and they lack the yellowish tinge of the latter. They have 

 a smooth, thick wall and granular protoplasmic contents, together with a 

 large central oil drop, and a highly refractive body, probably containing 

 the nucleus. They closely resemble, except in size, the ripe oospores of 

 Phytophthora erythroseptica. 



In most of the cases in which the attempt was made, these spores were 

 successfully germinated, and the mode of germination in its early stages 

 exactly resembles that described for the oospores of P. erythroseptica (5). 

 When, however, the germ-tubes had reached a length equal to about three 

 times the diameter of the spore, growth either ceased at once or soon after 

 the formation of a terminal swollen body into which the contents of the 

 germ-tube passed. In some cases this body sent out a germ-tube of its own 

 • which reached a length of several times that of its own diameter, and then 

 ceased to develop further. In no case was mycelium, bearing sporangia of 

 any sort, produced from these spores ; hence it is not possible to say with 

 certainty to what fungus they belonged. 



Attempts were made to raise cultures from the germinating spores, but 

 these failed, owing either to the early death of the germ- tubes or to serious 

 contamination of the medium with bacteria ; for it was naturally impossible 

 to obtain these spores from the diseased host plant free from contamination. 



