18 DISEASES OF FIELD & GARDEN CROPS. [CH. 



bodies, varying in size from a grain of sand to that of a 

 small bean. An affected potato stein is illustrated, 

 natural size, at A, Fig. 3, and a section through a part of 

 a similar stem is illustrated at B to show the black 

 nodular growths in situ. The small black bodies here 

 drawn are at first white, at length they become externally 

 brown, and ultimately black ; they are hard and compact, 

 and, owing to their hardness, they have been termed 

 Sclerotia from sJderos, hard. One of these bodies sur- 

 rounded by spawn threads is shown, twice its natural 

 size, at Fig. 4. These nodular growths when examined 



-X-2- 



FIG. 4. 



Sclerotium of Peziza postuma, B. and Wils. 

 Twice the natural size. 



with the microscope are found to consist of highly con- 

 densed and compacted spawn cells or mycelium, white 

 in the centre and gradually getting black (through brown) 

 towards the outside. When an excessively thin slice is 

 taken off a cut surface of one of these nodules and magni- 

 fied 400 diameters, the appearance is similar with the 

 illustration at Fig. 5 ; here the gradual change of colour 

 from the white internal cells to the black thick -walled 

 outer ones is illustrated, together with the felted statum 

 of white mycelial threads, on the top of illustration, in 

 which the Sclerotia are embedded. 



Sclerotia, or compacted masses of fungus spawn in a 

 resting state, are common amongst fungi ; some examples 



