112 RESEARCHES ON FUNGI 



The ecological significance of the inhibitory action of light on 

 tiny fruit-body rudiments will be pointed out in the Section on the 

 mechanical fixation of the fruit-body. 



The Morphogenic Effect of Light on Developing Fruit-bodies. 

 — Light, in addition to exercising an inhibiting action upon the 

 growth of tiny fruit-body rudiments, gives a morphogenic stimulus 

 to young fruit-bodies, i.e. causes an alteration in their form. How- 

 ever, this moulding action of light is confined to the base of the 

 stipe and does not affect the main shaft of the stipe or the pileus. 

 In order to perceive the morphogenic effect of light it is necessary 

 to compare the growth of two fruit-bodies in two cultures, one of 

 which (like Culture A in the last Section) is top-lighted (Fig. 59, 

 p. 106), and the other of which (like Culture C) has been kept in 

 complete darkness (Figs. 61, 62, and 66 ; pp. 109, 110, and 116). 

 In both light and darkness the pileus develops equally well and sheds 

 spores in about equal abundance (for a mature fruit-body grown 

 in complete darkness, vide Fig. 66) ; but there is a difference in 

 the structure of the stipe. A fruit-body in a top -lighted culture, 

 as we have seen, arises on the darkened lower surface of a dung- 

 ball ; but, in response to the stimulus of gravity, it soon pushes its 

 way upwards between the dung-balls. Its rudimentary pileus is 

 thus soon brought into the light. As a result of the young fruit- 

 body receiving light in this way, the base of the stipe — and by this 

 is meant the solid part of the stipe, which will henceforth be called 

 the stipe-base — becomes somewhat bulbous and, as a rule, does not 

 attain a greater axial length than about 1 cm. (Figs. 63, B, and D ; 



64, B ; and 65, A). On the other hand, a fruit-body which has 

 been grown in complete darkness, wherever it may have arisen — 

 at the top, bottom, or side of a dung-ball — has a solid stipe-base 

 which, instead of being bulbous and only about 1 cm, in length, is 

 always much elongated and 3-4 cm. in length (Figs. 63, F ; 64, D ; 



65, B and C ; and 66). There is therefore a marked contrast 

 between the form of a stipe-base of a fruit-body which has under- 

 gone most of its development in the light, and that of a fruit-body 

 which has developed in complete darkness. 



An elongated stipe-base of Coprinus sterquilinus is in reality a 

 short and simple pseudorhiza of exactly the same morphological 



