Pethybuidge — Observations on Phytophthora erythroseptica. 187 



spherical part of the oogonium. The wall itself not infrequently shows, in 

 optical section, a series of radial striations, which, in surface view, present 

 the appearance of pits of narrow diameter. The contents consist of a large 

 central oil-Jrop (sometimes two or more smaller ones), staining almost black 

 with osmic acid, surrounded by a periplieral mass of very finely granular 

 protoplasm, in which is a rather large, refractive, oval body. This body 

 also becomes fairly deeply stained with osmic acid, more so than the proto- 

 plasm in which it is embedded, but less so than the central oil-drop. Figs. 

 1 and 2, Plate XIII, show ripe oospores both in a living condition and after 

 fixation with osmic acid vapour. 



The ripe oospore has never been seen (except after artificial treatment) 

 free from the oogonium and its permanently attached antheridium either in 

 pure cultures or in material gathered in the field. It is, however, of course 

 possible that during the winter the remains of the antheridium and oogonium 

 may become disintegrated in the soil, thus setting the oospore free. 



]\licro- Chemical Reactions of the Walls of the Sexual Organs. — When the 

 ripe sexual organs are treated with chlor-zinc-iodide solution, the empty 

 hyphae, the antheridial wall, and that of the lower part of the oogonial 

 funnel, including the hyaline plug, immediately become coloured purplish- 

 violet, which later deepens somewhat to a claret colour. The oogonial wall 

 with its included oospore becomes of a faint bluish tinge distinct from that 

 of the antheridium. 



With sulphuric acid and iodine in potassium iodide the same colour is 

 produced in the hyphae, antheridial wall, base of funnel and plug, but 

 practically no change takes place, at least for a considerable time, in the. 

 oogonium proper and its contained oospore. 



If, however, gentle pressure be brought to bear on tlie cover-glass so as to 

 burst the oogonium, the following changes occur rapidly with both of the 

 reagents named, viz., the hyphae, antheridial wall, lower part of oogonial 

 funnel and plug stain as before ; the oogonial wall is of somewhat the same 

 tinge, but not quite so deep, and around its periphery a very fine yellowish 

 line can be made out; the thick wall of the oospore becomes a distinct blue 

 colour with no tinge of red in it, quite distinct from the tint of the antheri- 

 dium, &c. ; while, if it is itself squashed, it is also seen (particularly clearly at 

 the points of cleavage) to be surrounded by a very fine yellow line. 



The walls of both the oogonium and the oospore are therefore seen to be 

 each of a double nature. This fact is clearly demonstrated by the action of 

 concentrated sulphuric acid on them. When this reagent is applied, the 

 oospore, including its wall, swells up, tlie contents are destroyed (except the 



SCIENT. PROfi. K.D.S., VOL. XIV., NO. X. 2 F 



