FOMES APPLANATUS 147 



applanatus fruit-body are to reach infectible wounds in a forest, 

 they must be produced by the million. 



When a tree has received a serious wound, the way is usually 

 open for the attack on the wood, not by one wood-destroying fungus 

 only but by several. Which species, other things being equal, is 

 the one most likely to infect a new wound first ? Surely the one 

 that has the most numerous spores floating about in the air, for the 

 spores of such a fungus are likely to settle on the wound first. The 

 success of one species of wood-destroying fungus rather than another 

 in infecting a particular wound and thus occupying the new sub- 

 stratum to the exclusion of competitors, may often be simply a 

 question of a few hoars or days of priority in spore-arrival. 



Which individual Fomes applanatus plants are most likely to 

 give rise to successful progeny ? Other things being equal, surely 

 those which develop fruit-bodies most freely and the' fruit-bodies 

 of which have the maximum efficiency in producing spores ; for, the 

 more spores a plant produces, the greater will be its chance of beating 

 its competitors of the same species in the struggle for existence. 



In order to occupy a new wound-surface successfully, it is advan- 

 tageous for any fungus plant to deposit on that surface as many 

 spores as possible, for thereby the wound will become infected in 

 many places, and, from the first, a vigorous mycelium will be 

 present. This is all to the good in the struggle for existence of the 

 plant with other fungus plants either of the same species or of other 

 species. It may therefore be said that, other things being equal, 

 the more spores a given fungus plant can cause to settle on a given 

 infectible wound-surface, the greater will be the chance of survival 

 for its progeny. We thus again perceive an advantage in such a 

 fungus as Fomes applanatus producing vast numbers of spores. 



From the experiments made by Kniep x and others 2 with about 

 thirty diverse species, it seems probable that the majority of 

 Hymenomycetes, like the majority of Mucorineae, are heterothallic. 

 It is also known that in heterothallic species of Hymenomycetes 



1 Hans Kniep, " "Dber morphologische und physiologische Geschlechts-differen- 

 /ierung," Verhandl. der Physikal.-med. Gesellschajt zu Wurzburg, 1919, pp. 12, 13. 



2 Irene Mounce, " Homothallism and Heterothallkm in the Genus Coprinus,' 

 Trans. Brit. Myc. Soc., vol. vii, 1922, pp. 256-269. 



