192 Trans. Acad. JSci. of St. Louis. 



to this effect.* The wind sweeping through a tree catches 

 hold of the long strands hanging from the branches and tears 

 off pieces, which are carried to other trees. To find how and 

 where the wind can tear the thallus various tests were made.f 

 Several masses were weighed dry, and again after being 

 soaked in distilled water. The latter was removed as com- 

 pletely as possible from the lichen by means of filter paper. 

 Two trials showed: — 



Weight of mass dry = 3.8 grs. 3.97 grs. 



Weight soaked 12 hrs. =13.3 grs. 11.5 grs., 



that is, the mass increased about three times in weight, which 

 is probably below what it would be during a heavy rain. The 

 threads are very elastic when wet, stretching 30-50% of their 

 original length before breaking. The next test was to de- 

 termine the longitudinal breaking strength. It was somewhat 

 difficult to attach weights to the thread, and after some trials, 

 wire hooks were inserted into loops tied into the ends of the 

 threads, to one of which a scale pan with weights was attached. 

 A number of threads were selected, as nearly as possible of 

 the same diameter, but as this method is of course not very 

 exact, the results can have only a relative value. 



When dry the filaments broke at: When soaked 12 hours : 

 198 gr. 28 gr. 



109 gr. 23 gr. 



144 gr. 27 gr, 



130 gr. 25 gr. 



Threads of Usnea barbata, var. ceratina gave these results : — 



When dry : When soaked 30 minutes : 



224.6 gr. 53.5 gr. 



266.0 gr. 43.0 gr. 



* Schiraper (Die epiptiytische Vegetation Amerikas: 31) says that birds 

 frequently use the strands of Tillandsia usneoides for building nests and 

 thus spread the plant. 



t Tests made with Bamalina reticulata are omitted as they have already 

 been given by G. J. Peirce, On the mode of Dissemination and on the 

 reticulations of Bamalina reticulata. Bot. Gazette 25 : 404. 1898. 



