430 B idler, — The Reactions of the Fruit-Bodies of 
of the rod becomes rounded and grows directly into the pileus. The latter 
is gymnocarpous from the beginning and never forms a gill-chamber. 
When rods which have been growing in weak light are placed in strong 
light they form pilei. The younger and more vigorous the rod, the 
quicker will the pileus be formed, and the larger it will be. Older and less 
vigorous rods, when placed in strong light, can only be induced to slowly 
form very small pilei. 
It has been pointed out (p. 428) that, until the pileus begins to develop, 
the stipe shows no trace of any reaction to the stimulus of gravity, and its 
direction of growth is completely controlled by the light. When, however, 
the pileus has attained a breadth of about a centimetre, an important 
change sets in. The end of the stipe becomes strongly negatively geotropic, 
so that it takes up a vertical position even in strong oblique light. At this 
stage the stipe appears to be no longer responsive to heliotropic stimuli. 
The change of physiological properties in the stipe may be compared 
to changes which take place in certain organs of the higher plants during 
their development. Thus the peduncle of the Poppy ( Papaver ) is positively 
geotropic whilst the flower is in the bud, but becomes negatively geotropic 
during flowering and fruiting. The peduncle of Tussilago Farfara also 
shows reversal of its geotropic properties. Whilst flowering it is negatively 
geotropic. During the development of its fruit the upper part of the 
peduncle becomes positively geotropic. The final change occurs upon 
the ripening of the fruit, when the whole peduncle becomes negatively 
geotropic 1 . Similar instances might be adduced for heliotropism. I am not 
aware, however, of any case among the higher plants where the direction of 
development of an organ is at first entirely controlled by the stimulus 
of light and afterwards by the stimulus of gravity. 
The following experiment serves to illustrate the negative geotropism 
of the end of the stipe. The stipe of a fruit-body had become vertical by 
bending through an angle of 45 0 (Fig. 1). The block, upon which the fruit- 
body grew, was then turned through a right angle so that the top of the 
stipe was placed in a horizontal position (Fig. 2). In three days the stipe 
had become vertical once more (Fig. 3). The block was then turned 
through a further right angle (Fig. 4). In the course of four days the end 
of the stipe had again executed a movement tending to place the end of 
the stipe in a vertical position. Owing to cessation of growth, however, the 
pileus had only been turned through an angle of 45 0 (Fig. 5). In all, during 
the two experiments, the stipe had moved round through an angle of 135°. 
Another nearly mature fruit-body was placed on its side in the dark. 
The pileus became partially erected and turned upwards through an angle 
of 30° in two days (compare Figs. 7 and 8). By this time all growth had 
ceased. The experiment indicates that the erection of the pileus is not due 
1 Vochting, Bewegungen der Blutlien und Friichte, Bonn, 1882. 
