THE SPHAEROBOLUS GUN 349 



the fruit-body : (1) morphogenically, i.e. by causing it, from the 

 first, to develop, as does the fertilised egg in the Fucaceae, 1 with its 

 apex directed toward the source of light ; (2) heliotropically, i.e. by 

 causing it to turn its apex after this has been formed, toward the 

 light by means of unequal lateral growth ; and (3) first of all morpho- 

 genically and then, if the direction of the light should be altered, 

 heliotropically. Further experiment alone can teach us which of 

 these three possibilities corresponds to the facts of nature. 



Light is a decisive factor in the time of opening of the fruit- 

 bodies ; for, in artificial cultures exposed to daylight in the labora- 

 tory, a certain number of fruit-bodies come to maturity each day 

 and discharge their glebal masses in the morning or noon hours, 

 and no discharges take place at night. This diurnal periodicity is 

 precisely similar to that of the sporangiophores of Pilobolus and of 

 the asci of a fruit-body of Ascobolus immersus. 



Bright sunlight, according to Miss Walker, 2 promotes the vigour 

 with which Sphaerobolus guns discharge their projectiles ; and, as 

 already suggested, this may possibly be due to light favourably 

 affecting the transformation of glycogen into sugar. 



We thus see that light acts on Sphaerobolus in several different 

 ways : (1) it is essential for fruit-body formation, (2) it causes the 

 fruit-body to develop so that its apex faces the strongest incident 

 rays, (3) it causes the fruit-body to open in the day instead of 

 at night, and (4) it increases the vigour with which a fruit-body 

 discharges its projectile. 



Sphaerobolus as a Coprophilous Fungus dispersed by Herbivorous 

 Animals. — Sphaerobolus is most frequently found on stumps, sticks, 

 boards and other pieces of worked wood, sacking, etc. ; and system- 

 atists, as a rule, have described it as lignicolous. Thus Dr. T. Petch, 

 writing to me concerning his observations in England, says : 'I 

 know the fungus well and used to find it until I was tired of seeing 



1 Hans Winkler, " Ueber den Einfluss ausserer Factoren auf die Theilung der 

 Eier von Cystosira barbata," Ber. d. D. Bot. Gesell, Bd. XVIII, 1900, pp. 298-305. 

 Winkler showed that the first cell-wall of the fertilised egg is formed perpendicularly 

 to the incident rays of light, and that the daughter-cell facing the light produces the 

 free branching system while the daughter-cell away from the light produces the 

 rhizoids. 



2 Vide supra, p. 321. 



