642 Scientific Proceedings, Royal Dublin Society. 



very thiu, and if the medium used be one not too rich in food, the growth 

 will be mainly in one plane (approximately), observation of the developing 

 organs will not be hindered by the growth of too luxuriant an amount of 

 mycelium, and can be carried on for a long period of time. It is also possible 

 to lift and replace after a short interval such cover-glasses with the films on 

 them without interfering with the growth on the film, and thus provide for 

 the aeration of the moist chamber in which the development is going on. 



Another very useful method of preparing film-cultures which was 

 employed was to pour rather less of a suitable gelatine or agar medium than 

 is usually employed for " plating out " into a sterile Petri dish which was 

 then slanted, so that the greater part of the medium flowed to one side of the 

 dish before it had time to set. The fungus was planted, after solidification 

 of the medium had occurred, on the part of the dish from which the latter 

 had flowed away, but of which a very thin film still remained on the surface. 

 The progress of growth of the fungus was watched under the lower powers of 

 the microscope through the bottom of the dish ; and when the desired stages 

 appeared to have been readied, these were studied in detail under high powers 

 by removing the lid of the dish, placing a drop of water on the desired area, 

 and covering with a cover-glass in the Visual manner. Such films were found 

 useful, more particularly in studying the final stages in the development of 

 tlie oospores, which were not always reached in the films on cover-glasses. 



On examining some of the mycelium taken from, say, a growth on sterile 

 potato-stalks, the sexual organs present are seen to^consist frequently of what 

 appears to be at first sight a single body, shaped somewhat like an inverted 

 figure 8, but not so strongly constricted in the middle, and having apparently no 

 wall there, and composed of two unequal-sized approximately spherical portions, 

 the smaller of which alone appears to be connected with the mycelium, both 

 being filled with densely granulated protoplasm. In some cases the contents 

 of the larger portion may have rounded themselves off and formed a spore 

 around which a thick wall may have developed, while those of the lower 

 may have become disorganized or have disappeared, revealing within it a 

 funnel or V-shaped structure, the apex of which is situated at the point of 

 attachment of the 8-shaped body to the mycelium, while the broader base 

 extends across it at the point of constriction. The various details of the 

 work involved in the elucidation of the structure and development of these 

 8-shaped bodies need not be described here, but on the observations made the 

 following general account of the characters of the sexual organs of the fungus 

 is based. 



The antheridia and oogouia are produced on separate hyphae, which, 

 although they may be branches of the same mass of mycelium, do not arise 



