198 Trans. Acad. Sci. of St. Louis. 



ing winds, and that these sides are usually dead. It is of 

 course possible that that side died first for some reason and 

 that the lichens then became attached. But it will be evident 

 that in the case of Usnea barbata the selective reasons for 

 becoming attached to a living branch are not the same as for 

 lichens which become firmly attached. There can be no 

 selective action on the part of the wind, which carries pieces 

 alike to dead and living branches; and as has been said, such 

 pieces are more likely to hold fast to living branches, be- 

 cause of the leaves. It does not seem probable that the mere 

 fact of its being a healthy branch can determine whether the 

 lichen shall live there or not. Only a large number of 

 observations will definitely settle this point. 



Issued December 17, 1898. 



