314 Howe: Preliminary notes on the genus Usnea 



bringing about a new selective scattering, which seems the most 

 likely solution, as old herbarium specimens become in time rust- 

 red. This dichrolc condition is at best very difficult of explana- 

 tion. My friend Mr. Edward Mallinckrodt, of the Mallinckrodt 

 Chemical Works, writes me in reply to a request of mine to 



investigate this coloration : 



"The color is no doubt due to some change of an organic dye 

 contained in the plant, not to any mineral substances and hence 

 the difficulty in analyzing it, as we are easily able to handle min- 

 eral substances but not organic. You are no doubt aware that a 

 good deal has been written upon the subject of red leaves without 

 any consensus of opinion as to the cause, if I am properly in- 

 formed. If I were sure that at the end of a month or so work on 

 the lichen would lead to definite results, I might take it up 

 although all of our men are pretty busy and outside problems are 

 hardly in order, but as a matter of fact unless your lichen is an 

 exception it contains a Jiumber of plant substances, which are 

 pretty closely related and difficult to identify. Even if we got 

 these out w^e would still be unable to put our finger on this one 

 and say that its behavior in a test-tube accounts for the color 

 change in the plant. The whole trouble is that with organic com- 

 pounds nature works such extremely obscure changes that the 

 chemist in the laboratory can hardly follow them. Analysis, 

 therefore, is extremely difficult in this case, while comparatively 

 easy in the case of mineral or inorganic products." 



Usnea barbata fiorida occurs on living deciduous trees, more 

 rarely on conifers (degenerate on other substrata), throughout New 

 England, save, iij a broad sense, in the upper Canadian zone. It 

 attains its greatest luxuriance in sw^amps, or in shaded and moist 

 situations. In such places almost every plant found will be heavily 

 fruited, whereas in drier localities only a few plants comparatively 

 will bear apothecia, giving us proof that the remaining plants are 

 sterile examples o{ fiorida^ zxiA should not be classed under a 

 separate species, or even subspecies. 



Usnea barbata Florida (L.) Fr., f. strigosa Ach. 



This form, not recognized in Tuckerman's Synopsis of 1882, 

 but included in the one of 1848, is a contingent form oi florida, 



*See Nylander, loc. cit. 265: *« Color rubiginosus interdum obviens vix nisi 

 maceratione ortus, nee typicus (inde quoque in Usnea Jlorida oritur var. rubiginea 

 Mich., ut animadvertit Eschweiler). 



