THE DETERMINATION OF LICHENS IN 

 THE FIELD. 



By W. Watson, D.Sc. 



It is often very useful to the ecologist to be able to nauie the 

 lichens he finds in a particular association, and the following kev is 

 intended to help in that direction. By it many genei-a and some 

 species of British licliens may be determined in the field, stress being- 

 laid on characters which can be seen by the naked eye or with the 

 aid of a lens, though spoi-e characters are often added for the sake of 

 completeness. Even with the aid of such a key (an artificial one, 

 since it takes little account of lines of classiHcation), the determina- 

 tion of the genus of a lichen is not always possible in the field since 

 so many genera have their distinguishing characters in microscojjic 

 details such as the form, colour, and septation of spores. The 

 character of the algal symbiont can often onh^ be rightly determined 

 by microscopic examination, but in a general way its colour is indi- 

 cated by the colour of the thallus as shown in surface view, or in 

 a rough section more or less parallel to the surface. A gelatinous or 

 bluish thallus usually contains blue-green algae, whilst a yellow, grev, 

 white, or green thallus usually indicates the presence of green algae, 

 and some experience in the field often enables the algal constituent to 

 be diagnosed correctly. In some cases the colour of the thallus is 

 almost a generic indication, as in the vivid green colours shown by 

 the thalli of Pelt idea, Coriscium, and Solorina saccata when they 

 are moist. 



The equipment of a field-lichenologist should include a small 

 case containing tubes of potassium hydrate solution (equal weights of 

 caustic potash and water) and strong calcium hypochlorite solution, 

 wdth dipping rods. The case can be made of such a size and form so 

 as to remain upright in one of the U23per waistcoat pockets. A 

 similar tube of strong iodine solution in potassium iodide is also 

 useful in some cases. 



I have used the following abbreviations: — -Ap. = Apothecium. 

 C = Chloride of lime (bleaching-povyder) solution, C— indicating no 

 reaction when the thallus is treated with the solution, and C-|- a 

 positive one. K = Caustic potash solution, K— indicating the absence 

 of a colour reaction and K-l- a positive reaction. I=iodine solution 

 in pot. iod. Sp. = spore. Th. =Thallus. Usu. = usually. ± stands 

 for more or less, or when affixed to K or C for positive or negative, 

 thus Kit means that either a positive or a negative reaction is shown 

 after treatment with caustic potash. /x. = micromillimetre or j-^-^-^ of 

 a millimetre. 



Journal of Botany, 19-2. [Supplement I.] h 



-V ^— 



