CHAPTER XIII 



THE SPECIFIC GRAVITY OF SPORES 



THE measurements described in this and the following chapter 

 were made chiefly with the object of testing Stokes' Law. 



In order to determine the specific gravity of spores, the heavy- 

 fluid method was employed. Owing to the minute size of the spores 

 and' their very slow rate of fall even in water, and also in order 

 to reduce convection currents to the least possible minimum, it 

 was found necessary to use a special small chamber with which 

 to carry out the tests. After several chambers had been tried, 

 the most suitable one proved to be an ordinary Leitz-Wetzlar 

 counting apparatus, such as is used for estimating the number of 

 blood-corpuscles in drops of blood. In the chamber in question 

 the distance between the cover-glass and the central disc is only 

 0*1 mm. 



The mode of procedure in making the experiments was as 

 follows : A fresh fungus was obtained, and its pileus was cut off 

 and placed on a piece of glass or paper, where, in the course of 

 a few minutes or hours, a spore-deposit collected. Some drops 

 of the solution to be tested, namely, calcium chloride of known 

 specific gravity, were then poured into a small beaker. Spore 

 masses were scraped up from the spore-deposit with a needle 

 and placed in the solution. This was then stirred vigorously, so 

 that the spores became well separated and fairly evenly suspended 

 in it. A drop of the fluid containing the spores was next placed 

 in the Leitz-Wetzlar apparatus and the cover-glass applied. If 

 the spores were heavier than the medium in which they were 

 suspended, they gradually sank and collected on the bottom of 

 the chamber. If they were lighter, they gradually rose and 

 collected beneath the cover-glass. The end-result by this means 

 could usually be determined in a few minutes. Convection currents 



