ADAPTATIONS IN ASCOBOLUS 257 



ripening of the asci is of such a kind that each morning a few 

 asci go through their final phases of stretching and discharge their 

 spores almost simultaneously about midday or in the early after- 

 noon. After one series of asci has exploded, another immediately 

 begins to develop Avhich will discharge its spores on the following 

 day. Owing to this periodic development of successive series of 

 asci, the asci always come to maturity in daylight, i.e. they always 

 go through their final stretching at a time when their direction 

 of growth can be controlled by heliotropic stimuli. The positive 

 heliotropism of the asci causes these structures — the fungus guns — 

 to become directed toward well-lighted positions and therefore in 

 general toward open spaces. When the spore-masses are shot 

 outwards, they thus come to have a good chance of avoiding 

 obstacles in their flight through the air. The orientation of the 

 asci must prevent a very large number of spores from being wasted 

 by being shot against adjacent dung balls, &c. We thus see that 

 the protrusion of the ripe asci, their periodic development, and 

 their heliotropism are intimately correlated with one another. The 

 great violence of spore-discharge is associated with the unusually 

 large size of the asci and of the spores. The clinging of the spores 

 together during discharge and the large mass of the projectile, as 

 we have already seen, are significant in that they enable the spores 

 to be shot to a greater distance from the horse-dung balls than 

 would otherwise be possible. The ascospores are thrown to such 

 a distance that they fall on the surrounding herbage, where they 

 can be devoured by herbivorous animals and thus find their way 

 into faeces. 



Lycoperdon. — In Gastromycetes the modes of spore-dispersion 

 are of various kinds. Sphieroholus stellatus has a wonderful 

 catapult mechanism for casting a sac containing spores a dis- 

 tance of several inches. In the Phalloidei,^ the fruit-bodies 

 are specialised for attracting flies by means of form, colour, 

 scent, and sweet juices. In the Tuberacese, the hypogean 

 Truftles, &c., are eagerly sought for by certain quadrupeds and 

 other animals. The main facts in these instances are now 

 well known and recognised. However, a few remarks may be 



1 T. W. Fulton, loc. cit. 



B 



