258 



The Plant World 



The excessive length of species of Usnea in some regions is 

 directly due to their having never been disturbed; for example, 

 Usnea longissima reaches a length of six or seven meters in the 

 forests of Baron Rothschild's estate in Hungary, where an axe 

 has not been allowed for more than one hundred and fifty years; 

 here in California it is ten or twelve feet long only in the redwood 

 forest not yet visited by the lumberman, where it grows upon 

 trees which are from 500 to 1,500 years old. The author also be- 

 lieves that the greater size of many California lichens may be 

 due to the prolonged growing season, though of course this can 

 only be settled by careful measurements and extended series of 

 observations. 



A number of European investigators and a few Americans 

 have made valuable contributions to the physiology of lichens, 

 but the field is still almost a virgin one. Relatively few exact 

 morphological studies have been completed, and the researches 

 of Stahl and Sturgis stand almost alone in the investigation of 

 the sexual reproduction of lichens. The tissues of most li- 

 chens do not readily lend themselves to the niceties of killing, 

 fixing, staining, and sectioning, and some of the published papers 

 have been ridiculous from the slip-shod methods used. But 

 ways may be found of overcoming most of the difficulties, and 

 here again the field is clear for the pioneer. Of course in the 

 above has not been included the masterly investigations into the 

 thalline structure conducted by DeBary, Schwendener, Bornet, 

 and others Enough has been said, however, to show that there 

 is a very extensive field for physiological and morphological in- 

 vestigators. 



The ecological study of lichens is a most fascinating depart- 

 ment of plant ecology and they illustrate very well the influences 

 of varying conditions of temperature, light, and moisture. 

 Professor Bruce Fink has done most valuable pioneer work in 

 this line. Too many students of phytogeography have altogether 

 neglected lichens, taking for granted that they had no ecological 

 significance, but this is a great mistake. But the writer wishes 

 to say that it is also a mistake to rush into ecological work until 

 there has first been acquired a thorough and exact knowledge of 

 the organisms studied. By all means take up ecology. But 



