INHIBITORY EFFECT OF LIGHT 



III 



time they have brought their upper ends into the hght, they are 

 too advanced to be influenced adversely by its action ; they there- 

 fore continue their further development unchecked. A rudiment 

 which has succeeded in passing through what, so far as light is 

 concerned, may be called its critical stage of development can after- 

 wards withstand unharmed even strong sunlight. Should one 

 find a full-grown fruit-body on a dung-mass in nature, one would 

 be justified, therefore, in making the following reflection upon it. 

 The fruit-body must have origin- 

 ated in a dark or dimly -lighted 

 recess of the substratum, for other- 

 wise the sun's light would have 

 inhibited its development when it 

 was a tiny rudiment. How- 

 ever, by the time it had grown 

 sufficiently large to push upwards 

 into the light, owing to an internal 

 change in itself, it had become 

 immune to the sun's inhibitory 

 action. Hence, the later stages of 

 its development took place freely 

 in the light. 



FiG: 63. — Coprinus sterquilinus. Comparison 

 of two fruit-bodies grown in daylight 

 with an equal-aged fruit-body grown 

 in the dark ; to illustrate the fact that 

 light inhibits the lengthening of the 

 solid stipe-base. A and C, grown in the 

 light ; E, grown in total darkness. B, 

 D, and F, vertical sections of A, C, and 

 E respectively ; a, the solid stipe- base ; 

 b, the hollow stipe-shaft. Cultuie 

 medium, sterilised horse-dung balls. 

 The fruit-bodies A and C soon pushed 

 up into the li'ght, and therefore their 

 stipe-base is relatively short and the 

 pileus relatively advanced in develop- 

 ment. The fruit-body E, owing to the 

 absence of the inhibitory action of light, 

 has continued to elongate its stipe-base, 

 and its pileus is relatively very rudi- 

 mentary. The pilei of the fruit-bodies 

 A and C would expand about three days 

 before the pileus of the fruit-body E. 

 Natural size. 



