362 RESEARCHES ON FUNGI 



bolus consists of the slimy products of the innermost layer of the 

 peridium which partly deliquesces as the projectile is prepared for 

 discharge. The adhesive matter of the projectiles of the three 

 fungi under discussion, therefore, while having an identical function, 

 comes into existence, from the developmental point of view, in three 

 different ways. 



(4) Heliotropism of the Guns. The sporangiophore of Pilobolus 

 and the asci of Ascobolus immersus are positively heliotropic (Fig. 1 72, 

 a and b). In unilateral light they execute a turning movement, so 

 that in the end they come to point their apices in the direction of 

 the source of strongest illumination. The fruit-body of Sphaerobolus 

 also develops so that its apex faces the strongest incident rays of 

 light (Fig. 172, c), but whether light stimulates the young fruit- 

 body morphogenically or heliotropically remains to be decided by 

 further investigation. Since the Pilobolus, Ascobolus immersus. 

 and Sphaerobolus guns all point in the direction of the source of the 

 strongest light, they all shoot their projectiles in the direction of the 

 source of the strongest light. 



The turning of the gun toward the light is accomplished : in 

 Pilobolus by the bending of the sporangiophore under the influence 

 of a light stimulus received by the subsporangial swelling ; in 

 Ascobolus immersus by the bending of the sporangium, i.e. of the 

 ascus ; and in Sphaerobolus by the fruit-body as a whole either 

 morphogenically or heliotropically. Thus, in the three fungi under 

 discussion, the structures which turn toward the light and so enable 

 the projectiles to be shot toward the light, are very different morpho- 

 logically. 



(5) Multisporous Nature of the Projectile and the Non-separation 

 of the Spores whilst the Projectile is attached to Herbage. The Pilo- 

 bolus, Ascobolus immersus, and Sphaerobolus projectiles are all 

 multisporous, and the spores (spores and gemmae in Sphaerobolus) 

 cannot separate from one another without the help of some special 

 external agent. Neither the wind nor the rain nor both combined 

 can set free the spores from the projectile of which they form a part. 



The numerous spores in the projectile of Pilobolus are prevented 

 from escaping owing to their being enclosed in part by a tough and 

 persistent sporangial wall, in part by a thick and insoluble gela- 



