THE TRANSLOCATION OF PROTOPLASM 143 



either with ordinary or with dark-field illumination. When water 

 flows through a glass tube, one can see nothing of its motion because 

 there are no visible particles in it. There was therefore the possi- 

 bility that, even if protoplasm were streaming rapidly through a 

 hypha of G. sterquilinus or C. lagopus, one would not be able to 

 detect its flow. 



The mycelial hyphae of Coprinus sterquilinus and of C. lagopus, 

 relatively to those of Fimetaria fimicola and Pyronema confluens in 

 which streaming has actually been observed, not only have a hyaline 

 instead of a granular cytoplasm but are also very thin. In a further 

 attempt to observe streaming in the Hymenomycetes, a hymeno- 

 mycetous species with thicker hyphae and more granular protoplasm 

 than in Coprini was sought, and the desired material was found in 

 Rhizoctonia solani. 



Rhizoctonia solani is the cause of the black scurf and stem canker 

 disease of potato tubers. The "dirt that will not wash off" on 

 affected tubers consists of small black sclerotia. Although the 

 fungus is often placed in the Fungi Imperfecti, it is now well known 

 that, under favourable conditions in the field, it gives rise to a 

 thelephoraceous fructification, known as Corticium solani, which 

 produces basidia in abundance. I myself have seen these fructifi- 

 cations around the base of living potato stems at Kew, England. 

 The strain of R. solani used was kindly supplied by my colleague, 

 Dr. G. R. Bisby, who had isolated it from soil in the course of his 

 studies of the soil fungi of Manitoba. 



The young vegetative hyphae of Rhizoctonia solani are often 

 about 8 fi thick, have colourless walls, and are septate at intervals 

 of 100-200 fx. The cytoplasm is not quite hyaline, for it is very 

 faintly clouded with fine almost imperceptible particles. The 

 vacuoles resemble those of Pyronema confluens : they arise peri- 

 pherally and remain attached to the cell- wall. The septa all have 

 a small central pore, 1 [i or less in diameter, through which a bridge 

 of protoplasm passes (Fig. 54, B, p. 99). 



A hanging drop of cleared dung-agar was inoculated with 

 mycelium from a stock culture of Rhizoctonia solani. On the 

 following day the hyphae, which had grown outwards to the peri- 

 phery of the drop, were illuminated by daylight and examined with 



