COPRINUS CURTUS 25 



but will come to perfection and shed their spores in the dark. If, 

 however, fruit-bodies have been deprived of light not only on the 

 day they should shed their spores but also on the previous day, they 

 are unable to elongate their stipes to the full extent, their pilei do 

 not open, and no spores are developed. 



So far as the periodicity in fruit-body development is concerned, 

 the experiments point to the alternation of day and night as being 

 the controlling factor. The final maturation of each fruit-body, as 

 we have seen, is absolutely dependent on the action of light on the 

 fruit-body when this is in a rudimentary stage of development, 

 and we may conclude that it is the light on the day previous to 

 pilear expansion, i.e. on the penultimate day, which provides the 

 stimulus which enables a fruit-body to enter on its final develop- 

 ment, a development which, when once started, can go on in 

 the absence of light and which happens to attain its climax — 

 the discharge of the spores — during the morning of the next 

 day. 



The Stipe. — The stipe, by means of intercalary growth in a 

 region just beneath the pileus, begins to elongate during the after- 

 noon of the day before the pileus expands and, at this time and 

 until the next morning, it is positively heliotropic and ageotropic 

 (Vol. I, p. 70, Fig. 26, D). At about 10 a.m. the next morning, just 

 before the pileus begins to expand, the top of the stipe ceases to 

 be positively heliotropic and becomes negatively geotropic, with 

 the result that the pileus is turned gradually upwards until its 

 central axis is in a vertical line (Vol. I, p. 70, Fig. 26, E). This 

 response of the stipe to heliotropic and geotropic stimuli in suc- 

 cession results in the pileus being first pushed out from crevices 

 between dung-balls into the open and then set in the best position 

 for spore-discharge.^ 



Just before a pileus is about to open, the top of the stipe is 

 extremely sensitive to the stimulus of gravity. If one turns a 

 fruit-body from a vertical to a horizontal position, the stipe begins 

 to turn up the pileus within about three minutes after first receiving 

 the geotropic stimulus.^ Before the pileus comes to rest in a 

 perfectly upright position, it may be swung by the stipe several 

 1 These Researches, vol. i, 1909, pp. 69-70. 



