3 2 



mals to require no further elucidation of the subject here. Another 

 and but little known phase of this subject is the antagonistic symbi- 

 osis of fungi with lichens, and of lichens with lichens, and with 

 mosses. We shall now consider these relations somewhat more in 

 detail. 



I. ANTAGONISTIC SYMBIOSIS OF FUNGI WITH LICHENS. 



There are no natural reasons why this form of symbiosis should 

 not be of frequent occurrence, although no special study has been 

 made of the subject. It is also very likely that many so-called para- 

 sitic lichens are in reality parasitic fungi. A number of herbarium 

 specimens described as parasitic lichens proved, on closer study, to be 

 fungi ; in no case could a thallus be detected. It was also evident 

 that these parasitic fungi (Ascomycetes) had an injurious effect upon 

 the algae of the lichen-thallus, as they were nearly all destroyed in 

 the immediate vicinity of the fungus. As far as it has been possible 

 to observe, these parasitic fungi usually occur on the .upper surface of 

 the lichen-thallus, quite rarely on the lower surface, as in Endo- 

 carpon miniatum. It is a comparatively difficult matter to study the 

 organic union of the symbionts, since the hyphal threads of both are 

 very similar. This difficulty we do not encounter where fungi are 

 parasitic upon higher plants. I have repeatedly made careful sec- 

 tions through host and parasite and employed various staining meth- 

 ods, but did not succeed in demonstrating definitely that the hyphal 

 network of the supposed parasite was or was not continuous with that 

 of the host. By crushing methods, assisted by various alkaline sol- 

 vents, one can readily separate the two symbionts, but this is not in- 

 contestible evidence that they were not organically united. This 

 difficulty of investigation also applies to the so-called pycnidia and 

 spermagonia. But since we are certain that there are ascomycetous 

 fungi parasitic upon lichens, so, likewise, in regard to sper- 

 magonia and pycnidia it is reasonable to assume that they are 

 parasitic fungi, especially since it has not been conclusively demon- 

 strated that they are male reproductive organs. It is also reasonable 

 to assume that the parasitic fungi of lichens are morphologically and 

 physiologically different from the same forms of parasitic fungi of 

 higher plants, a variation induced by a marked difference in the sub- 

 strata. Even leaving out of consideration the spermagonia, which we 

 shall discuss more in detail in another chapter, parasitic fungi are 



