34 



of the host or hosts. Minks is also inclined to believe that the so- 

 called " protothallus " is simply the remnant of a host-lichen. Al- 

 though it is questionable whether syntrophy is of as frequent occur- 

 rence as Minks supposes, there is no doubt that it does occur, not 

 only among the lower lichens, but among the higher forms as well. 

 I have found a species of Lecanora growing upon a Cotlema-thallus. 

 There are many undecided problems connected with this form of 

 symbiosis. No one has as yet been able to observe the complete 

 course of development of this form of parasitism ; that it is parasitism 

 is quite certain. I have not adopted the term syntrophy proposed by 

 Minks, since it indicates nothing which is not already implied by the 

 term parasitism or antagonistic symbiosis. 



3. ANTAGONISTIC SYMBIOSIS OF LICHENS WITH MOSSES. 



According to Bonnier (n) certain lichens, Lecidea vernalis in 

 particular, live parasitically upon the protonema of mosses. This 

 author has made numerous culture experiments to verify his obser- 

 vations. He placed moss and lichen spores upon sterilized substrata, 

 where their development could be readily observed. It was found 

 that the hyphal filaments formed a mycelium about the protonema, 

 even entering the cells, where they formed a dense network, causing 

 the protonemal cell to become considerably enlarged. ' It is evi- 

 dently a form of antagonistic symbiosis, because the protonema is 

 killed in a short time. Bonnier has observed this antagonistic sym- 

 biosis of lichens in different genera of mosses. Lichens also occur 

 parasitically upon the leaves and other parts of mosses, as well as 

 upon higher plants. Practically nothing is known of the life-his- 

 tory of lichens parasitic upon higher chlorophyll-bearing plants, 

 although they are numerous and have been known for a long time. 

 They are mostly low forms of lichens and occur principally in tropi- 

 cal regions. Many of the occurrences of supposed antagonistic 

 symbiosis require further study. There is little doubt that many of 

 the injurious effects supposed to be due to antagonistic symbiosis of 

 lichens is, in reality, caused by mechanical interference. For in- 

 stance, a lichen spreading over a moss, which is of frequent occur- 

 rence, cuts off sunlight as well as air, thus having an injurious effect 

 in an indirect way. It is generally admitted by the leading investi- 

 gators that the lower forms of lichens, in particular, take very little 



