THE PILOBOLUS GUN AND ITS PROJECTILE 143 



been harvested in this way, the sap was poured into a watch-glass 

 and covered with a sheet of glass to check evaporation. 



The microscope employed had a mechanical and revolving stage 

 and a micrometer in its eye-piece ; 

 and it was fitted with lenses which 

 gave a magnification of 40. The Petri 

 dishes containing slides, tubes, and 

 water were set on the stage of the 

 microscope and the lengths of the 

 five central drops in each tube were 

 read and recorded in succession. With 

 very little practice it was found possible 

 to measure the lengths of the drops 

 with accuracy and rapidity. The appear- 

 ance of the scale of the micrometer, 

 when applied to a drop for its measure- 

 ment, is shown in Fig. 69. 



In carrying out the experiment 

 with the Pilo bolus cell-sap, I received, 

 and here wish to acknowledge with 

 my best thanks, valuable assistance 

 from my friend and former pupil. 

 Dr. W. F. Hanna. He prepared the 

 standard solutions of sugar and filled 

 the capillary tubes, etc. ; I harvested 

 the cell-sap just before it was re- 

 quired for use and kept the watch- 

 glass which contained it covered 

 except when a drop was being drawn 

 from it ; and we both took part in 

 measuring and recording the lengths 

 of the drops after the tubes had been 

 sealed and placed in water. 



The standard solution employed for comparing with the sap 

 was sucrose. Of this substance a stock solution of 34-2 grams 

 in 100 cc. distilled water, i.e. a weight-normal solution, was 

 prepared. This solution, at a temperature of 20° C, has an 



Fig. 70. — FUobolus longipes on 

 horse dung. The dung, 

 taken fresh from a stable, 

 was placed in a covered 

 crystallising di.sh. The 

 pliotograph shows part of 

 the culture four days later. 

 There are about 500 fruit- 

 bodies in view. Magnifica- 

 tion, 1 • 3. 



