208 PHYTOPHTHORA PARASITICA. 



time with cupric ammonium hydrate the outer wall is dissolved. 

 After this treatment iodine and phosphoric acid stains the central 

 thick wall quite yellow and the interior of the conidium appears 

 filled with a blue mass, possibly the dissolved inner wall. If in 

 place of strong cupric ammonium hydrate a weak solution of this 

 reagent is used for a short time, remnants of the outer thin wall are 

 visible and they stain blue with the cellulose colour reagents. 

 Evidently the thicker central yellow wall is of quite a different 

 chemical composition from the other two, which are shown to be 

 of cellulose. Ruthenium red, acidified Bismark brown and alum 

 hematoxylin stain the " resting" conidia not very sharply without 

 any previous treatment, on account of the outer coat of cellulose 

 on which these stains have no effect. But when the outer wall is 

 dissolved by cupric ammonium hydrate, acidified Bismark brown 

 stains the central wall brown, which colour is not washed out by 

 hydrochloric acid, while alum hematoxylin stains it violet blue very 

 clearly. Mangin gives these stains as specific reagents for compound 

 pectic substances. Ammonia and alkali carbonates have not any 

 action on the thick yellow coloured central wall and therefore it 

 is not composed of pure pectose, but of some compound pectic 

 substance. When treated with sulphuric acid the central wall 

 remains undissolved, even after a long treatment, while the two other 

 walls are completely dissolved in a short time ; caustic potash 

 does not immediately dissolve it. These reactions clearly prove 

 the absence of callose from the walls of " resting " conidia. 



The composition of the antheridial wall is quite simple. It is 

 constituted of pure cellulose without any callose. It is immediately 

 dissolved by sulphuric acid and cupric ammonium hydrate ; 

 ammonia, caustic alkalies and caustic carbonates have no action on 

 it ; it readily stains blue with all the cellulose colour reagents. 



The walls of the unfertilised oogonium are composed of pure 

 cellulose. After fertilisation the oogonial wall undergoes modi- 

 fication. In the Peronosforacece investigated by Mangin 1 , the 



1 Mangin, L. Recherches sur les Peronosporees. Bull. Soc. d'Hist. Nat. d'Autun, VIII, 

 1895, p. 99. 



