PethybriCge — Observations on Pliytophthora erythroseptica. 183 



bearing the conidia as well as those of the hyphae, making up the main 

 mass of mycelium, are composed apparently of cellulose, seeing that they 

 stain a purplish-violet colour when treated with chlor-ziuc-iodide, or with 

 sulphuric acid and iodine in potassium iodide.' 



When conidia are placed in either chlor-zinc-iodide solution or in sulphuric 

 acid and iodine in potassium iodide, their walls become stained a purplish- 

 violet colour (indicating the presence of cellulose), with the exception of the 

 thicker and more hyaline apical portions, which do not become stained at all 

 by tliese two reagents. No traces of any yellow colouration of the walls or 

 portions of them can be observed. 



When placed in concentrated sulphuric acid, the conidia swell up and 

 burst ; and the contents, with the exception of the oil-drops, quickly dis- 

 appear. The walls, excepting the apical portions, are rapidly dissolved ; but 

 very careful observation shows that they are rarely or never completely 

 destroyed, although the remains of them become so exceedingly thin as to 

 be easily overlooked. The apical portions of the conidial walls are con- 

 siderably more resistant to the action of the strong acid, although they also 

 become to some slight extent dissolved. 



When placed without previous treatment in a solution of ammoniacal 

 copper hydrate, the conidia usually burst, and the walls slowly dissolve. 

 Even after standing for a fortnight, liowever, traces of the walls can still be 

 discerned, and the apical portions are scarcely, if at all, affected by this 

 reagent. 



It would, therefore, appear that the conidial wall is composed largely of 

 cellulose, but that its apical portion consists of some substance other than 

 cellulose, which possibly forms an extremely thin outer layer over the 

 remaining portions of the wall. 



Germination of the Conidia. In the former paper it was stated that 

 conidia might give rise to hyphae, and also (in a foot-note) that typical 

 zoospores had been observed^ ; and the production on germination of germ- 

 tubes direct, as well as of zoospores, has since been abundantly confirmed 

 many times. 



' Dastur states that he found these two reagents not very reliable for cellulose reactions in the case 

 of F. parasitica, and he placed more reliance on the action of calcium-chloride-iodide and phosphoric 

 acid and iodine, as recommended by Mangin. The chlor-zinc-iodide used for P. erythroseptica was 

 an old solution (almost certainly over thirteen years old), and concentrated sulphuric acid diluted 

 with an equal volume of water was used along with iodine in potassium iodide, both reagents giving 

 satisfactory results. These reagents, as well as the ammoniacal copper hydrate solutions (prepared 

 from metalUe copper and ammonium hydrate, as well as from copper sulphate, sodium hydrate, and 

 ammonia), were tested, and found to work satisfactorily with cotton-wool and pure Swedish 

 filter-paper. 



^ With a fatal facility for error, Massee {loc. cit.) makes the whoUy erroneous statement, " As 

 to whether the conidia produce zoospores or a germ-tube on germination is not known, . . ." 



