262 RESEARCHES OX FUNGI 



found to be 20; in Fomes vegetus 148 for one year, and 500 for three; 

 whilst in a large and old specimen of Fomes igniarius it proved to be 

 nearly 1000. 



The crowding of the gills and the reduction in diameter of the tubes in 

 certain fruit-bodies {e.g. those of the Mushroom and of Fomes igniarius), 

 after allowing for a small margin of safety, appear to have reached their 

 limits consistent with the violent horizontal discharge of the spores from 

 the basidia. 



Chapter III. — The fruit-bodies of most species of Hymenomycete- are 

 very rigid. This rigidity is of considerable importance in keeping the 

 axes of the tubes of Polyporea?, the planes of the gills of Agaricinea^, &c, 

 in vertical positions. Slight swaying movements cause loss of spores. In 

 a Mushroom it was calculated that, when two adjacent gills are tilted from 

 their vertical planes to an angle greater than the critical angle of about 

 2° 30', some of the spores are unable to escape from the interlamellar 

 spaces. With a tilt of about 5°, half the spores are lost; and with a tilt 

 of about 9° 30', four-fifths of them. The rigidity of stipes in many species 

 is secured by hollow cylindrical form and by unequal tensions in the layers 

 of cells. 



Chapter IV. — The growth movements of a fruit-body can be regarded 

 as so many adjustments of a delicate machine made with the object of 

 placing the hymenium in the best possible position for liberating the spores. 

 A Mushroom and the ephemeral, coprophilous Coprini exhibit four such 

 adjustments, and Polyporu* squamosus five. The nature of the adjustments 

 is correlated with the general structure of the fruit-bodies and with the 

 orientation of the substratum. 



The amount of eccentricity of the pileus of Polypwus sguamosus is con- 

 trolled by a morphogenic stimulus of gravity. 



The stipes of certain ephemeral Coprini, just before the pilei expand, 

 are extremely sensitive to the stimulus of gravity. When a stipe had been 

 changed from the vertical to the horizontal position, a distinct upward 

 curvature was noticed after a stimulation of 1'5 minutes. Another stipe, 

 similarly displaced, gave a distinct macroscopic reaction to the stimulus of 

 gravity after 3 minutes' stimulation, and turned through a complete right 

 angle, so as to regain a vertical position, in 17-5 minutes. The last 80° 

 were turned through with a greater angular velocity than that of the 

 minute-hand of a clock. This angular velocity is far greater than that 

 known for any Phanerogam, or indeed any other plant organ when stimu- 

 lated by gravity. 



Chapter V. — In perfectly still air, the spores liberated from a pileus 

 placed above a horizontal sheet of paper fall vertically downwards and 



