TILLETIA TRITICI 217 



In the present investigation, the following was the method 

 employed for germinating the chlamydospores under sterile con- 

 ditions. 



With a pair of sterile forceps having somewhat flattened arms 

 a mature bunt-ball is carefully removed from between the glumes 

 of an intact bunted head of wheat. The cover of a sterile Petri dish 

 is then raised and the bunt-ball is crushed with the forceps, so that 

 the spores fall in a heap in the centre of the dish while the seed- 

 coat is still held with the forceps. The seed-coat, which of course 

 may be contaminated on its exterior surface by the spores of other 

 fungi, is then thrown away. Altogether four to six bunt-balls 

 taken from as many bunted heads are treated in the manner just 

 described, and the spores from all the crushed bunt-balls are caused 

 to accumulate in a single heap in the Petri dish. The mixing of 

 the spores from several bunted heads goes far to ensure that at 

 least some of the spores will germinate readily. With a sharply- 

 pointed sterile scalpel some spores are now removed from the heap 

 in the Petri dish and distributed sparsely over the surface of a plate 

 containing freshly-poured, non-nutrient, 1-5-2-0 per cent. agar. 

 Instead of plain agar, 2-5 per cent, malt-extract agar may be used, 

 but plain agar has the advantage in that it keeps moulds and 

 bacteria in check. To keep the air above the spores moist, the plate 

 (with its cover on) is then set on a low stand (an inverted Petri-dish 

 cover) in a large crystallising dish (22 x 9 cm.) containing a thin 

 layer of water. The crystallising dish is then almost, but not quite, 

 covered with a sheet of glass, an aperture being left for ventilation. 

 The whole is set on a table and incubation allowed to proceed at 

 room temperature (18°-20°C). 



In from three to six days, under the conditions just described, 

 the sculptured outer wall of the chlamydospores ruptures, while the 

 inner wall begins to protrude as a germ-tube or promycelium 

 (Fig. 107, B). The average width of the promycelium is about 8 /n, 

 while the length is very variable. Sometimes the promycelium 

 becomes only 20 n in length, i.e. scarcely longer than the diameter 

 of the chlamydospore ; while, at other times, specially when there 

 is a surface water-film, it may attain an extreme length of about 

 0-5 mm. Growth in length is apical. At first the promycelium is 



