26 



dual nature of lichens. They also demonstrated that this association 

 was not like that of ordinary parasitism, but rather formed a union 

 for mutual benefit, thus enabling these plants to exist where neither of 

 the components could exist alone. This association was known as 

 cqnsortism (Reinke), or symbiosis (de Bary). 



There were also a large number of investigators engaged in the 

 study of the morphology as well as the physiology of particular groups 

 of lichens as well as of lichens in general. We will mention a few of 

 these. Stahl (89, 90) made a special study of the spermagonia. His ' 

 conclusions were that in Collema the spermatia are the male reproduc- 

 tive organs. The female reproductive organ known as the carpogone 

 after being fertilized by the spermatia develops into the apothecium. 

 It is interesting to note that this form of sexual reproduction was ob- 

 served only in Collema. Recently Sturgis has apparently verified 

 Stahl's results (93). Further investigations are necessary to estab- 

 lish Stahl's theory. A number of investigators have demonstrated 

 that the spermatia will develop a hyphal network, even developing 

 new spermagonia. This would seem to prove that spermatia are true 

 spores instead of sexual organs. The most important work in re- 

 gard to the physiology of lichens was done by Jumelle (44). This 

 author gave us the first reliable results of observations made on the 

 exchanges of gases in fruticose and foliose as well as in crustaceous 

 lichens. He found that the exchange of O for C0 2 is independent of 

 the substratum and dependent upon sunlight and moisture, and also- 

 that this gaseous exchange varies greatly in different lichens. An 

 excess of moisture reduces carbon-assimilation. Respiration in some 

 lichens still goes on at very low temperatures, — io° to — 40 C. 

 Lichens can also resist much higher temperatures than phanerogams. 

 For instance, respiration was still active when the lichen was exposed, 

 for one day to a temperature of 45° C, three hours at 50 C. and 

 one-half hour at 6o° C. 



Among the systematists we will mention Tuckerman, 1 who con- 

 sidered Korber's system the most useful and adopted it in his classifica- 

 tion of the North American lichens ; his diagnoses are carefully 

 given, accompanied by spore-measurements. With Nylander he 

 considered the spermagonia of great importance in classification. A 

 number of new species were described. He also issued a work 



•Tuckerman, E. Synopsis of North American Lichens. Parti. 1882. Part II. 

 1888. 



