ON THE MODE OF DISSEMINATION OF USNEA 



BARB AT A.* 



Hermann von Schrenk. 



In many places along the North Atlantic coast one comes 

 across tracts of forest in which a large number of the trees 

 are covered with the common gray lichen, Usnea barbata and 

 its varieties. This lichen often covers the trees entirely, 

 giving them a sort of hoary appearance ; where many such 

 trees stand close together, especially if they happen to be 

 conifers, the effect is truly a gloomy and somber one. The 

 question has frequently occured why so many of the trees 

 should be dead, and so universally covered with large masses 

 of the lichen, and the notes following are to record some of 

 the observations made in the Middle and North Atlantic 

 States. 



The species of Usnea are found all over the world, grow- 

 ing in nearly all cases on trees. Two forms may be distin- 

 guished. In the more common and well known, a central 

 main stem of the thallus is firmly attached to the wood or 

 bark, and forms a small clump or bush. The other type is 

 that represented by such forms as Usnea barbata dasypoga, 

 Usnea longissima, etc., in which the thallus as a unit has little 

 or no connection with the branch or tree upon which it rests. 

 These forms are truly epiphytic, and free from any suspicion 

 of absorbing even small and insignificant quantities of food 

 substances from their substratum. It is with this type that 

 the following deals. The thallus consists of long threads, 

 some as much as 20 inches in length, branching freely both 



* Presented before the Academy of Science of St. Louis in preliminary 

 form Dec. 21, 1896 (Trans. 7: lxi.), and, by title, Dec. 6, 1898. 



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