436 Buller . — The Reactions of the Fruit-Bodies of 
to the surface of the mycelial layer on which they develop. Their formation 
takes place equally well in light and darkness. 
Before the development of the pileus, the stipe is perfectly indifferent 
to geotropic stimuli. In the absence of light it is rectipetal, and in its 
presence positively heliotropic. 
In the absence of light the stipe may continue to grow for weeks 
or months, and may attain a length of six or more inches, but no signs 
of a pileus make their appearance. The development of the pileus depends 
on the presence of sufficient illumination. Grown in the dark, therefore, 
the fruit-bodies are all monstrous and abortive. 
Whilst the pileus is developing, the stipe alters its reactions to external 
stimuli. It becomes negatively geotropic and ceases to be heliotropic. 
The pileus is sometimes developed unequally in fruit-bodies with 
oblique stipes. The longest gills are always found on the side continuous 
with the lower side of the stipe. The inequality of development is induced 
by the stimulus of gravity. 
The gills begin their development in such manner as to become 
perpendicular to the surface of the pileus from which they are formed. 
They are never heliotropic, but become positively geotropic. 
Fruit- bodies grown in weak light are prone to branching and often 
become grotesque. Branching is often induced by the formation of abortive 
pilei. 
It may be shown that the reactions of the fruit-bodies to external 
stimuli are admirably adapted for the economical distribution of the spores. 
DESCRIPTION OF THE FIGURES IN PLATES 
XXIII, XXIV AND XXV. 
Illustrating Professor Bulter’s paper on Lentinus lepideus. 
PHOTOGRAPHS. 
Figs. 1-5. Nat. size. All the same fruit-body and illustrating reaction to geotropic stimuli. 
Fig. 1. The stipe grew towards the light at an angle of about 45 0 with the vertical. When the 
pileus began to develop the end of the stipe became negatively geotropic y and curved upwards 
through an angle of 45 0 so as to become vertical as in figure. 
Fig. 2. The fruit-body grown in the position shown in Fig. 1 was turned through a right angle 
so as to assume the position shown in this figure. 
Fig. 3. The same fruit-body after three days. The end of the stipe had curved through a right 
angle so as to bring the pileus into the erect position once more. 
Fig. 4. The fruit-body was then turned through another right angle so as to take up the 
position shown in this figure. 
Fig. 5. The same fruit-body after four days. The end of the stipe has turned through an angle 
of 45 0 and growth has ceased. The pileus is, therefore, only partially brought into the erect position. 
The gills have all curved towards the earth. 
