THE MORPHOGENIC EFFECT OF LIGHT 115 



very small (Figs. 63, F, and 64, D) ; but, as soon as the 

 stipe-base has ceased to elongate, the pileus and contained stipe- 

 shaft commence to grow rapidly. Now let us suppose that two 

 fruit-bodies are grown in two cultures, one of which is top-lighted 

 and the other completely darkened. The fruit-body in the light 

 will soon complete the formation of its stipe-base, as this is rela- 

 tively short ; and it will then immediately proceed to the rapid 

 enlargement of its pileus. On the other hand, the fruit-body 

 grown in the dark will complete the formation of its stipe-base 

 relatively slowly, for this, as a rule, is some four or five times longer 

 than that of the fruit-body grown in the Ught (c/. in Fig. 63 B and 

 D with F, and in Fig. 64 B with D). By actual observation it was 

 found that, as a matter of fact, the development of the stipe-base 

 of a darkened fruit-body takes two or three days longer than that 

 of a top-lighted fruit-body. As soon as a darkened fruit-body has 

 completed the development of its long stipe-base, it, too, immedi- 

 ately proceeds to the rapid enlargement of its pileus. Finally, 

 the hollow shafts of the stipes and the pilei of both darkened and 

 top-lighted fruit-bodies become equally well developed (c/. in 

 Fig. 65 A with B and C ; also cf. Fig. 65, A, with Fig. 66) ; but a 

 comparison showed that a top-lighted fruit-body begins to shed 

 its spores some two or three days before a darkened fruit-body. 

 That a top-lighted fruit-body completes its whole development 

 2-3 days sooner than a darkened fruit-body appears to be solely 

 due to the fact that a darkened fruit-body spends 2-3 days longer 

 in the development of its stipe-base than a top-lighted fruit-body. 



Although light completely inhibits the further growth of tiny 

 rudiments exposed to its rays, yet, as we have just seen, light also 

 hastens the later development of a fruit-body as a whole. This 

 hastening, however, is simply due to the fact that light inhibits 

 the elongation of the stipe-base and so permits the growth-energy of 

 the fruit-body to be concentrated earher than would otherwise be 



Fig. 65 — cont. 



C differs from a fruit-body grown in the light (1) in developing on the upper 

 side of a dung-ball and (2) in having a solid stipe-base protruding above the 

 substratiun. The fruit-body C, owing to the abnormal conditions of its 

 development (absence of light), was insecurely fixed to its substratum, with 

 the result that it toppled over and finally broke off at its base (cf. Fig. 60). 

 Natural size. 



