176 RESEARCHES ON FUNGI 



of the tapping key with the left hand. The microscope was then 

 lowered with the right hand by means of a rackwork on the 

 stand so that the spore was still kept in view. When the field 

 arrived at the bottom of the compressor cell after having been 

 lowered in this way for about 8 mm., the spore crossed the lower 

 line of the field, whereupon a second drum contact was made. 

 The time of fall could therefore be calculated from the drum 

 record in the usual way. The distance of fall could be deter- 

 mined by adding to the distance between the upper and lower 

 lines of the field, namely 4'55 mm., the distance through which 

 the microscope had been lowered. The latter was found in each 

 case by reading a vertical scale which was situated on the 

 microscope stand and provided with a vernier. From the time 

 and distance data thus obtained the velocity of fall could be 

 calculated at once. 



Fifty measurements with the spores of Boletus felleus were made 

 in the manner just described. The average observed distance of 

 fall was 12-05 mm. and the average time required to fall through 

 it 10-57 seconds. Hence, the average velocity of fall through 

 12-05 mm. below the gills was 1-14 mm. per second. Doubtless by 

 this method the rate of fall of small particles might be measured 

 through greater distances than 12 mm. 



Whilst measuring the rates of fall of spores the magnification 

 was kept as low as practicable, so that the observed distance of 

 fall should be as large as possible. Under those conditions the 

 spores were seen merely as just visible specks, the shape of which 

 could not be determined. It seemed, however, of interest to 

 attampt to find out what positions the spores assumed whilst 

 falling. The magnification of the microscope, therefore, was 

 increased by using a No. 3 Leitz objective. Into the much 

 lessened field of view, spores in focus fell relatively less often, 

 and in passing across the field appeared to fall with a relatively 

 much greater velocity. However, the shape of the spores could 

 often be distinctly observed. It was found that the spores, whilst 

 falling the first few millimetres after leaving the gills, often turn 

 round and round upon themselves in an irregular manner. Longer 

 spores often oscillate from side to side and probably fall in very 



