188 Scientific Proceedings^ Royal Dublin Society. 



oil-drops), the inner and thicker part of its wall becomes dissolved, whilst 

 the inner portion of the oogonial wall does likewise. Finally there are left, 

 one within the other, two thin films, one being tlie outer part of the oospore 

 wall, and the other that of the oogonial wall. The upper part of the funnel- 

 shaped portion of the oogonial wall within the antheridium, and above the 

 hyaline plug, also resists the action of concentrated sulphuric aold. 



The outer part of the oogonial wall seems to differ slightly from that of 

 the oospore wall in that the former is impermeable or only very slowly 

 permeable to dilute sulphuric acid. It is for this reason that when the 

 intact sexual organs are treated with sulphuric acid and iodine in potassium 

 iodide the oogonial and the oospore walls do not become coloured. On the other 

 hand, the outer part of the oogonial wall is penetrated at once — to some 

 extent at least — by chlor-zinc-iodide solution; but the oospore wall stains more 

 quickly and more deeply blue with this reagent when the oospore is previously 

 artificially liberated from the oogonium, showing that the oogonial wall does 

 offer some resistance to this reagent. 



When the ripe sexual organs are placed, without pi'evious treatment, 

 in a freshly prepared solution of ammoniacal copper hydrate, the hypiiae, 

 antheridial wall, lower portion of oogonial funnel with its hyaline plug, 

 together with the inner portion of the spherical part of the oogonial wall, 

 become dissolved iu the course of a few days, leaving the intact oospore 

 surrounded by the slender outer part of the oogonial wall, which, as stated 

 above, resists the action of concentrated sulphuric acid, and is coloured 

 yellow with the iodine reagents mentioned. 



Oospores liberated from their oogonia artificially, when allowed to remain 

 in this reagent, show no signs whatever of the solution of their walls, even 

 after a period of twenty-one days ; neither does solution of the oospore 

 walls occur with this reagent when the oospore is burst, and the reagent 

 therefore iu a position to attack its walls from the inside as well as the 

 outside. 



Germination of the Oospores. — It has not been found possible to cause 

 germination to take place in only comparatively recently matured oospores ; 

 and the material on which the following description is based was derived 

 from nine months' old cultures on oat extract agar slants. Examination of 

 such slants reveals the occasional presence of already germinated oospores, 

 so that nine months must be regarded as more than the minimum period 

 of rest required. The stages iu germination to be described were observed 

 in hanging-drop preparations in sterilized bog-water at room-temperature, 

 They require a period of two or three days for their completion. 



