130 "Black Neck" or Wilt Disease of Asters 



9/x in diameter, and when young these are non-septate. In later stages 

 and especially in pure cultures septa appear irregularly. The hyphae 

 are multinucleate and have the nuclei disposed at fairly regular intervals 

 (Fig. 2). The structure of the nucleus is somewhat difficult to make out 

 even with the best nuclear stains, but it clearly contains a single 

 nucleolus (Fig. 6). In addition to the nuclei, the vacuolated cytoplasm 

 contains numerous regularly arranged granules which stain readily 

 with nuclear stains (Figs. 6 and 8). Tests with osmic acid and Scharlach 

 R indicated that these granules are not of the nature of fatty bodies. 

 The second of the tests showed fat in the vacuoles of the cytoplasm; 

 the deeply staining granules may therefore correspond to the chondrio- 

 somes described and figured by Lewitsky 1 in the young oogonia of 

 Cystopus Bliti. Further investigation will be necessary to show whether 

 such an interpretation is correct, but in this connection it is of interest 

 that the granules in question persist in the sporangia and zoospores 

 (Fig. 19). 



The walls of the hyphae and also of the sporangia are of pure cellulose 

 and are readily stained violet by Schultze's chlor-zinc-iodide solution. 

 This reaction afforded a ready means of recognising the fungus through- 

 out the investigation, especially when questions of comparison with 

 the Fusarium were being considered. The mycelium of the latter 

 stains a deep yellow with this reagent and is therefore readily distinguish- 

 able from the Phytophthora. 



Sporangia. 



The sporangia of this fungus have never been observed to be formed 

 except under water; in this respect the species resembles Phytophthora 

 omnivora (De Bary 2 ) and Ph. erythroseptica 3 recently described by 

 Pethybridge as causing the pink rot of potatoes. Prior to the forma- 

 tion of sporangia the vegetative hyphae in the host tissues turn outwards 

 and grow through and between the cells until they reach the epidermis 

 (Fig. 7). They pass through the epidermal cells but the cuticle (c) 

 apparently offers some temporary resistance to further progress for 

 each hypha then swells out into one or more rounded branches (Figs. 7 

 and 8). These gradually separate the cuticle from the epidermis 

 and often form characteristic sorus-like groups (Fig. 7). Each of the 



1 Berichte der Deutach. Bot. Qes. Bd. 31. E. '.». 1913. 2 Bot. Zeitung, 1882. 



3 Rotting of potatoes by a new .species of Phytophthora, Sci. Proc. Boy. Dublin Soc., 



1913. Further observations on Phytophthora erythroseptica, Sci. Proc. Boy. Dublin Soc, 

 1914. 



