264 



RESEARCHES ON FUNGI 



culture of the mycelium was made on a stiff 2-per-cent. agar medium 



in a Petri dish. When 

 the culture was about 

 ten days old, the myce- 

 lium had formed a thin 

 mat which was only 

 slightly raised above 

 the surface of the agar 

 (Kg. 132). At this 

 stage, two pieces of a 

 sterile glass slide of 

 known thickness were 

 placed one on each 

 side of the mat, and a 

 sterile cover-glass (Fig. 

 132, c) was laid upon 

 the pieces of glass so 

 that it formed a bridge 

 above the mycelium 

 below. The Petri-dish 

 cover was then replaced 

 and the whole covered 

 with a bell-jar. In 

 some of the experi- 

 ments, to support the 

 cover-glass, sterile por- 

 tions of sewing needles 

 of known diameter were 

 used instead of pieces of 

 glass slides. By using 

 pieces of glass or needles 

 of different thicknesses, 

 the cover-glass was set 

 in succession at different 

 heights above the my- 

 celium. Whenever a 

 basidiospore is shot 



Fig. 131. — Tilletia tritici. Observation of the fall 

 of basidiospores by the beam-of-light method. 

 A test-tube t containing a malt-agar slope a 

 with a mycelial mat m at its surface is held 

 inverted by a clamp c in front of a con- 

 centrated beam of light b b b passing from 

 a projection lantern through a bull's-eye 

 condenser held on the brass rod r. Spores, 

 after being discharged from their sterigmata, 

 fell down through the air of the test-tube and 

 could be seen individually with the naked 

 eye as they passed through the beam of light. 

 The spores shown in the beam of light are 

 diagrammatically enlarged. Apparatus, two- 

 thirds the natural size. 



