182 Scientific Proceedings ^ Royal Dublin Society. 



I. MiCRO-ClIEMICAL EeACTIONS OF THE WaLLS AND GeKMINATION OF THE 

 CONIDIA (ZoOSPOKANGIA). 



Production of Conidia. — It was stated in the former paper that, with 

 possible exceptions in one or two isolated instances, the conidia of this 

 fungus could only be obtained under water. It is just possible that in 

 nature they may be produced in a saturated atmosphere, in contact with a 

 moist substratum such as on dead underground tissues ; but they are certainly 

 not produced on aerial conidiophores, as is the case, for instance, in P. infestans. 

 Essentially they are of an aquatic type, and are not subject to aerial 

 dissemination. They have not even been seen to become detached from the 

 hyphae bearing them, and they germinate while still attached to the latter. 



They are easily obtained in considerable quantities when a small piece of 

 medium, such as oat extract agar, on which the fungus is growing is 

 submerged in water (preferably previously sterilized) in a small flask. They 

 can also be obtained easily if small pieces of an affected tuber (in which the 

 disease has not proceeded so far that the killed tissues are already invaded by 

 saprophytes) are removed aseptically and placed in previously sterilized water. 

 Bog water or the watery extract of a boggy soil has been found excellent 

 for the purpose.' In the course of a few days at room-temperature 

 mycelium (bearing both conidia and sexual organs) can be seen emanating 

 from the pieces of media or tissue introduced. 



The mode of origin of the conidia, as well as their general shape, was also 

 described in the former paper. They do not possess an apical papilla, as is 

 the ease in P. infestans and some other species ; but tlie apex is more or less 

 blunt or even somewhat flattened. The contents when ripe are finely 

 granulated ; and usually a large oil-drop — sometimes two or more — occupies a 

 position in the centre. At the base, or rather at the end of the hypha bearing 

 the conidium, there is a somewhat large plug of cellulose, which effectually 

 shuts off the contents of the hypha from those of the conidium. 



Micro- Cliemical Reactions of the Cell-tvalls. — The walls of the hyphae 



' Incidentally, it may be remarked that this latter method of procedure forms a very satisfactory 

 method of diagnosing "Pink Rot" (the name suggested for the disease caused by this fungus in 

 potato-tubers) with certainty. Tbe affected tuber should be well washed, and, if in a particularly 

 dirty condition, may be disinfected externally by being placed for a short time in mercuric chloride 

 or formaldehyde solutions. It should, after drying, be cut open with a sterile knife, and small 

 portions of the diseased tissue should be removed as carefully and quickly as possible from a region 

 not near the skin and not far from the still healthy tissue, and dropped into sterile water in a small 

 flask, closed with cotton-wool. In a few days not only conidia, but also the characteristic sexual 

 organs of F. erythroseplica, will be produced. 



