TILLETIA TRITICI 245 



Buller 1 for S. roseus. Buller 2 also observed the germination of the 

 basidiospores of Puccinia graminis in situ, i.e. whilst they were still 

 seated on their sterigrnata. However, up to the present, in the 

 Hymenomycetes and the Uredineae, no undischarged basidiospores 

 have been seen to germinate basally like the one shown in Fig. 118 

 atgr. 



A Basidiospore-discharge Method of making Pure Cultures. — 

 Previous investigators who have sown chlamydospores from which 

 they have obtained a saprophytic mycelium may always have had 

 in their pure cultures a mixture of mycelia of two different origins : 

 (1) a mycelium derived directly from one or more H -shaped pairs 

 of sterigrnata (Fig. 114, B, p. 232), and (2) a mycelium derived from 

 basidiospores which have been borne on sterigrnata (Fig. 130, 

 C, p. 260). Taking advantage of the fact that basidiospores normally 

 are always shot away from their sterigrnata, the following simple 

 and convenient method of making pure cultures of basidiospore 

 origin only has been developed. 



Chlamydospores are germinated on 2 per cent, plain agar in a 

 Petri dish in the manner already described. 3 After six or seven 

 days, basidiospores are being actively produced on sterigrnata borne 

 on promycelia (Fig. 114, A, p. 232) and on sterigrnata borne on 

 mycelia (Fig. 114, B and D). The Petri-dish culture may now be 

 used for making another Petri-dish culture. 



The original Petri dish containing the fungus is inverted, so that 

 the agar looks downwards. The base of the dish is now held in the 

 right hand while the cover is removed with the left hand. The left 

 hand is now used to remove the cover from a freshly-poured malt- 

 agar plate of the same size as the first ; and then, with the right 

 hand, the original inverted plate-base is set directly over the new 

 plate-base, so that a single closed chamber is formed. To keep off 

 air-currents, the combination is now set on a sheet of glass and 

 covered with a small bell-jar (Fig. 119). 



Basidiospores continue to develop in large numbers at the sur- 

 face of the agar in the upper inverted Petri-dish base and, in due 



1 This volume of Researches, Fig. 91, p. 184. 



2 These Researches, Vol. Ill, 1924, p. 503, Fig. 203, h-l. 



3 Vide supra, p. 217. 



