The Growth of Usnea Longissima. 173 



CONDITIONS INFLUENCING THE GROWTH OF USNEA 



LONGISSIMA. 



By Elba R. Walker. 



I have been much interested in Mr. R. Heber Howe's 

 article (Plant World, 13:3, March, 1910) in which he questions 

 Mr. A. W. C. T. Herre's statements as to the eflfect of moisture 

 on the growth of Usneas. I have spent most of my life in 

 western Oregon, and, as I have seen Usnea longissima growing 

 in the Willamette valley it is always on trees near a swale or 

 stream, or in a low place where dew falls almost every night 

 during the dry season. It is peculiar in that it always forms a 

 very dense growth over one tree or a small group of trees and 

 no other specimens will be found within miles. It seems to 

 prefer localities quite protected from wind but not necessarily 

 where "not yet visited by the lumberman" (Herre). 



The finest growth of Usnea longissima I ever saw was found 

 about a mile from the little village of Cornelius, Washington 

 county, Oregon. It grew on a large vine maple {Acer circinatum) 

 tree surrounded by a few smaller ones overhanging a small 

 stream in a swale. This clump was a part of a narrow strip of 

 wood following the swale and bordered on either side at only a 

 distance of a few hundred yards by farm lands. Moreover, it 

 is at an altitude of only about 150 feet above sea level, which 

 is quite contrary to the statements of both Howe (Bull. Torr. 

 Bot. Club, 36:6) and Herre (Wash.. Acad, of Science, 12:2) who 

 say that it is found only at an altitude of 1200 to 1500 feet. 

 These authorities also speak of this Usnea only in evergreen 

 forests, while the specimens to which I refer grew on deciduous 

 trees. There are evergreens near by but none near enough to 

 produce any shade at this place. The Usnea longissima hung so 

 thickly from every limb of the group of trees that the space 

 beneath was partitioned, as by curtains. The threads hung 

 straight to the ground showing no sign of disturbance by wind. 

 In this place I removed numerous threads from 25 to 30 feet 

 in length, and one 33 feet in length I sent to Doctor Charles E. 

 Bessey of the University of Nebraska. The end of this and of 

 several other strands I had to pull from the higher limbs in such 



