BoT.— Vol. I.] PEIRCE— NATURE OF LICHENS. 209 



growth there must be great diversity. I am inchned to 

 believe that Rmnalina reticulata grows more rapidly than 

 most. My reasons are based on the universal occurrence 

 of large specimens all about here, and also upon the 

 behavior of this lichen in cultures. As emphasized by 

 Benecke (1898) in a recent paper on the culture of Algse, 

 and earlier by Moller (1887), the difficulty of excluding bac- 

 teria from cultures made from vegetating, and even from 

 spore, material, is very great. The presence of bacteria in 

 a culture will at least delay and obscure, if it does not 

 vitiate, the results; and yet to exclude the bacteria is 

 impossible with our present crude culture-technique. The 

 almost invariably gelatinous nature of the exterior of the 

 lichen body renders the removal of the bacteria from the 

 surface impossible. During the latter part of a long dry 

 season, the surface of such a lichen as Ramalina reticulata 

 must be so dry, at least by day, that it is not likely to hold 

 the bacteria or the fungus-spores that fall upon it, though 

 they may easily remain caught in some angle or slight 

 irregularity. During and for some time after a rain, in a 

 fog or on a dewy night, on the other hand, the gelatin- 

 ous surface will be moist, at least sufficiently so in spots to 

 cause whatever bacteria and fungus-spores fall upon it to 

 stick. Moller (1887) recommends washing as thoroughly 

 as possible in clean running water, the aim being to remove 

 by the stream, as well as by floating, whatever may have 

 fallen upon the surface. By this means he partially 

 cleansed the apothecia from which he intended to collect 

 spores for his cultures. 



Defective as such cleansing is for the apothecia, which 

 are not especially gelatinous on the surface, it is still more 

 so for the much more gelatinous surface of the thallus. 

 The running water does remove some of the foreign 

 objects, but some of the most gelatinous of these (for 

 example, bacteria in the vegetative condition) cling to the 

 gelatinous surface of the thallus in spite of the most thor- 

 ough attempts to dislodge them. For this reason, even if 

 sterilized water be used for the washing, a discourag- 

 ingly large proportion of the thallus fragments used for 



