372 SCIENCE PROGRESS 



touching and adhering to the sides. They thus reach the open 

 air in safety. Their rate of fall in still air was carefully 

 measured, and found to be about i mm. per second. Spore- 

 discharge lasts from five days to a fortnight. It is a con- 

 tinuous process, taking place night and day in dry and wet 

 weather. The spores are produced in vast abundance. With a 

 Leitz-Wetzlar counting apparatus it was calculated that each 

 hymenial tube in one instance had produced nearly 2,000,000. 

 The large fruit-body, already referred to, may well have given 

 rise to 10,000,000,000. From another fruit-body the spores were 

 liberated at the rate of about a million a minute. 



Notwithstanding the activity of spore-discharge from the 

 fruit-bodies of most Hymenomycetes, as a rule the falling spores 

 cannot be seen with the naked eye. Polyporus squamosus proved 

 to be a rare exception. The visibility of the discharge in this 

 instance appears to be due parti}'' to the great rate of spore- 

 liberation from the large fruit-bodies and partly to the large 

 size and colourless nature of the spores themselves. A fruit- 

 body, some 10 in. across, was grown on a log in an experimental 

 greenhouse where the air was very quiet. Under these con- 

 ditions clouds of spores, resembling steam or the finest white 

 smoke, were observed falling continuously for thirteen days. 

 The wreaths and curls of spores drifted slowly away from the 

 fruit-bodies, and became gradually lost at a distance of about 

 two yards. Wreaths of spores were distinctly seen on a black 

 background at a distance of 30 ft. 



The fruit-bodies of some wood-destroying fungi — e.g. Fomes 

 igniarius — are perennial. They are then very hard and of woody 

 or corky consistency, and produce new hymenial tubes and 

 spores each summer. They may continue their activity for ten 

 or more years. On the other hand, the comparatively soft 

 fruit-bodies of Polyporus squamosus are annual. They live but 

 a few weeks altogether, and soon die after the spores have been 

 discharged. 



The spores of Polyporus squamosus are dispersed by the 

 wind. As their rate of fall in still air is only about 1 mm. per 

 second, it will be readily conceived that slight breezes are able 

 to carry them very long distances before they settle. The 

 chances of a spore falling upon a suitable wound surface of a 

 tree, where germination and infection may take place, must be 

 extraordinarily slight. 



