von Schrenk — Dissemination of Usnea barbata. 191 



it conceivable how the wind alone could cause the branches 

 of the thallus to coil about the leaves and stem, and in- 

 tertwine in the way they do. The explanation I believe 

 lies in the fact that the branches are capable of a good 

 deal of motion when moistened unequally. When a fila- 

 ment is torn away, its branches are always more or less 

 bent and coiled. When moistened, the various branches 

 at first either straighten out or coil more, depending upon 

 the side which is wet first; after a few moments, the re- 

 verse motion takes place. The bending is due to the threads 

 of the medullary layer which absorb water readily and in- 

 crease some 10-15% in length, in the younger branches. If 

 then a filament is caught by a branch like that of the spruce, 

 it is first held simply by the diverging leaves. As it dries the 

 various branches curve about in almost as many directions as 

 there are branches, the tips describing arcs of 180° in many 

 cases. When equal drying has taken place the branches en- 

 deavor to get back to their original position. Oftentimes 

 they do, but far more frequently some other branch has 

 crossed over, or a leaf has been pushed aside by a contracting 

 filament, and in that way the branches are forced to assume 

 different positions from the one first occupied. Kepeated 

 wetting and drying brings about more coiling and uncoiling, 

 and ultimately such a tangle as is represented in the figure 

 results. Many a filament lodges on a branch, coils and un- 

 coils and is blown away again after a time, but on the whole 

 more filaments are firmly secured shortly after being caught. 

 I experimented with numerous pieces, which were placed on 

 spruce branches, and carefully watched. After about four 

 weeks the branches of the thallus were found firmly coiled 

 about the leaves of the spruce. A few days later the whole 

 piece might be off on another branch. (This was true only 

 of single filaments, and did not occur with larger masses.) 



The manner in which the lichen is disseminated is of inter- 

 est. The wind is the chief factor concerned, although I have 

 once seen birds using it for building their nest, and the lichen 

 seemed to be in good condition. It is extremely probable that 

 it is often carried by birds, but I have not seen any observations 



