264 THE PLANT WORLD. 



in sufficient quantity to manufacture the dyes in large quantities 

 for the markets. However, RocccUa tinctoria. a Hchen found on 

 our Pacific coast and on various coasts of the old world, produces 

 a pigment which has been known, by one name and another, since 

 earliest historic times. Orseille is one of the names applied to this 

 dye, and litmus is another name for it. This is no doubt the 

 " blue and purple " of the Old Testament, and in more recent 

 times the same dye was extensively used in France for coloring 

 silk. At the present time paper is colored with a neutral solution 

 of the dye and used commonly in chemical laboratories as litmus 

 paper. This paper forms a delicate test for acids and alkalis, the 

 acids coloring it red and the alkalis restoring the blue color. 

 Litmus is also found in the market as a carmine powder and as an 

 indigo-blue. In obtaining these lichen dyes, the thallus is pul- 

 verized, and then some alkali is applied to extract the dye. Litmus 

 is made chiefly in Holland. 



In closing, something should be said regarding the relation 

 of lichens to trees. In France and other countries of Europe, 

 foresters have supposed that lichens are injurious to the trees 

 and have to a limited extent practiced scraping the larger ones 

 from the bark, along with certain large fungi. However, it 

 will be seen readily enough that it would be difficult to accom- 

 plish much in this way in large forests, even were it known that 

 the lichens were very injurious to the trees. In our own country, 

 M. B. Waite, while experimenting with fungicides on fruit trees, 

 noted also that the Bordeaux mixture killed the lichens very 

 effectually. He was not at all certain that the lichens were in- 

 jurious to the trees, but thought that they might at least interfere 

 with the functions of the bark. It is true that the more conspicu- 

 ous foliose and fruticose lichens are more common on unhealthy 

 trees than on thrifty ones, but the question still remains as to 

 whether the lichens have worked injury to the trees, or whether 

 the unhealthy trees are more easily penetrated by the rhizoids 

 of the lichens. Also it may be that the unhealthy trees furn- 

 ish for tlie lichens some food material not present in the healthy 

 trees, or not so easily obtained as from the unhealthy ones. 

 In short, it probably is not worth while to take the time to re- 



