The Gray Bulb-Rot of Tulips 9 



the sclerotia, their fibrillose coating (Plate V, A) and the color changes 

 through which they pass remind one strongly of the sclerotia of both C. 

 vagum and C. stevensii. They differ from these species, however, in several 

 distinct respects. They are compact and definite in form like the sclerotia 

 of C. stevensii, instead of diffuse and crust-like as are the sclerotia of C. 

 vagum, though some other species of Rhizoctonia produce very definite, 

 more or less globose, sclerotia (Matz, 1921:15). The internal structure 

 is likewise different in certain respects. The cells of the medulla are more 

 globose and compact, showing little of the branched hyphal character 

 of the cells of the medulla of C. vagum and C. stevensii (Plate IV, B and C). 

 The large intercellular spaces so evident in the medulla of C. vagum are 

 almost entirely wanting. The cell walls are much less darkly colored, and 

 there is a distinct pseudorind which is entirely wanting in C. vagum. 

 If the structure of the sclerotium of S. tuliparum is compared with that 

 of C. stevensii, a somewhat more marked similarity is found. The descrip- 

 tion of the structure of the sclerotium of C. stevensii as given by Stevens 

 and Hall (1909:53) does not correspond exactly with the findings of the 

 present authors in an examination of specimens of the fungus sent to them 

 from North Carolina by F. A. Wolf. Stevens and Hall say: "They are 

 entirely devoid of any special epidermal structure, false epidermis, or 

 rind, the peripheral structure being identical with that of the interior." 

 The present authors find that the sections of C. stevensii show distinct evi- 

 dences of a pseudorind (Plate IV, B), due entirely, however, to the collapse 

 of the peripheral cells and not to a deeper coloration of the walls of these 

 cells. The cell walls of the sclerotial hyphae of C. stevensii are much darker 

 than those of S. tuliparum and uniformly tinted throughout. It is in the 

 collapsed character of the pseudorind that the two species show a similarity. 

 Stevens' drawing (Stevens and Hall, 1909:53, figure 6) gives the impres- 

 sion of thick walls in the cells of the medulla. The authors found that the 

 sections of C. stevensii show the walls to be thin, like those in C. vagum 

 and S. tuliparum. The cells of the medulla are more elongated (often 

 hyphal) than those of S. tuliparum, while the distinct intercellular spaces 

 so characteristic of the medulla of the sclerotia of C. vagum are much 

 less pronounced. On the whole, the structure of the sclerotium <>l > s '. 

 tuliparum approaches more nearly that of the sclerotium of C. stevensii 

 than it does that of C. vagum, though the last two are more alike. 



Furthermore, the characters of its mycelium (figures 1, 2, and 3). and its 

 behavior in culture (Plate III), confirm the writers' opinion that S. tuli- 

 parum is a Rhizoctonia. The branching of the mycelium and the barrel- 

 shaped cells, especially those of the loose hyphae covering the sclerotia, 

 are typically those of a Rhizoctonia. The reddish coloration of the media 

 by the growing mycelium is also a characteristic of many Rhizoctonias. 



No basidiomycetous stage has been discovered thus far, but the marked 

 similarity of the mycelium and the sclerotia to these structures in Rhizoc- 



