380 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of cells arranged in the form of a hollow ball." The recorded obser- 

 vation in this description that the ' ' spores ' ' have usually one or more 

 cavities on the surface communicating with the interior, is perhaps 

 highly suggestive of Spongospora, but Berkeley's statement that he 

 saw the organism in various stages of growth and attached to its flocci 

 is an important point of disagreement. Unfortunately the figures are 

 by no means definite, the drawings do not at all resemble the actual 

 spore-ball of Sp rngospora. 



As noted earlier in this paper (p. 377), in late stages of the disease, 

 and even in the powdery scab stage, the spore-balls or whatever spore- 

 balls remain in situ among the disorganized cells of the host are' 

 frequently intimately associated with the hyphse of various fungi. The 

 spore-balls appear sometimes to be attached to hyphse, or hyph^ 

 twine round them and often link them together. 



Under such circumstances it is not surprising that the " organism " 

 described by Berkeley should have been referred to the Ustilagineae. 

 But there are other considerations which introduce a certain element 

 of doubt as tO' whether Berkeley's figures really relate to the spore- 

 ball of Spongospora. During the winter 1909-1910, a number of 

 Hyphomycetous fungi appeared and flourished upon the surface of 

 some tubers which' had been kept in a damp atmosphere in the 

 Laboratory. Amongst these were forms of Verticilliuni, Stysanus, 

 Alternaria, Spondylocladium, and many others. After a time, 

 a number of structures of a golden-brown colour appeared among the 

 hyphse. For a long time it was not easy to be sure that these actually 

 belonged to conidial Hyphomycetous forms. But at length all stages* 

 in their development were observed in the case of Verticillium, and 

 similar structures w^ere definitely determined to be attached to the 

 hyphse of Stysanus. The fact that fungi producing structures closely 

 resembling the spore-balls formed by certain genera of Ustilagineae 

 occur on the potato, renders it a difficult matter to establish the 

 identity of the " organism " described and figured by Berkeley with. 

 Spongospora solani. 



The method of development of these structures is briefly as follows : 

 Short, septate, lateral hyphte grow out from the main filament. The 

 end cell or cells of the branch enlarge and become capable of stain- 

 ing more deeply than the remaining cells of the branch. These end- 

 cells then bend over, so that the branch has a crozier-like appearance. 

 The encircling non-staining cells form branch cells during the process 

 of coiling, so that the end-cells become enclosed in a jacket of hyphal 

 cells. Figs. 104 a-e illustrate the method of formation of these bodies 

 in the case of Verticillium. In fig. 104 a only one cell is sharply 

 marked off from the others, this cell has already bent over; 

 figs. 104 B-D show stages in the coiling process; figs. 104 e, f show liie 

 complete ball : in fig. 104 e only one special cell ; in fig. 104 f more 

 than one are enclosed. Figs. 104 g-i show similar bodies belonging to 

 Stysanus. The number of special cells enclosed in the ball seems to be 

 greater in the case of this Hyphomycete. Fig. 104 j relates to similar 



