262 RESEAKCHES ON FUNGI 



found to be 20; in Fowes vogetus 148 for one year, and 500 for three; 

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

 nearly lOOO. 



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

 certain fruit-bodies ('.//. those of the Musliroom 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. 



CHArTER III. — The fruit-bodies of most species of Hymenomycetes are 

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

 axes of the tubes of Polyporese, the planes of the gills of Agaricineie, &c., 

 in vertical positions. Slight swaying movements cause loss of spores. 1 n 

 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 layei'S 

 of cells. 



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

 as so many adjustments of a delicate machine made Avith 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 Polyporus 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 Pohjporus sguamoms 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 r5 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 



