THE DETERMT?fATTON OF LICHENS IN THE FIELD 27 



■10. Tb. determinate, smooth, greyish or whitish, 



subeffigiirate at the circumference Pertusaria lactea. 



Th. thin, effuse. (Also see L. prcerimata 



and L. illita.) Lecidea coarctata. 



Th. thick, white, pulverulent. On calcareous 



rocks Diploschistes candidus. 



•il. Th. (C — ) having a colour-reaction with 



iodine 42. 



Th. (C— ) not having a colour-reaction with 



iodine 45. 



42. Th. greyish, areolate, K4- yellowish, then 



red ; medulla bluish with iodine. On 



alpine mica-schist Aspicilia alpina. 



Th. K — , or only yellowing the medulla 43. 



43. Th. subdeterminate, usu. of dark areohe ; 



medulla reddish with iodine and yellowish 



with K \ Lecidea griseoatra. 



Th. whitish or greyish K — . Medulla vio- 

 let or dark violet with iodine. (Also see 

 L. prom/'nescrns) L. conflueiis. 



Th. K-. Medulla bluish with I 44. 



44. Th. and hypothallus whitish. Frequent L. cinerasceiis. 



Th. and hypothallus dark. Rare. 



L. tenebrans and L. atrofuscescens. 



45. Th. crimson or purplish with K Callopisma. 



Th. not crimson or purplish with K, though 



occasionally a reddish coloration comes 



after some time 4(3. 



46. Th. Avitli cephalodia (containing blue-green 



algse) Lecidea consentiens. 



Th. without cephalodia 47. 



47. Th. grey or dark (K— ) with a dark fimbriate 



marginal hypothallus. (Also see Rino- 



dina umhrinofusca and Lecanora prcepos- 



tera.) Rhizocarpon confervoides. 



Th. shining (as if oiled) dark, granulate- 



areolate, K— Lecanora badia. 



Th. greyish K+ yellow, then rusty-red Aspicilia cinerea. 



Sterile plants not having such characters are 



usu. not determinable. 



(«) Only a few lichens can be determined by this key, which only 

 gives rare lichens when they have fairly definite vegetative characters. 

 In some cases the plants included here are scarcely likely to be found 

 without reproductive organs. In some other cases the reproductive 

 organs are rarely found. 



{h) Clicenotheca centginosa is somewhat similar, but has a more 

 powdery th. and is a much rarer plant. 



(c) Lecanora symmicta is similar, but has a more determinate 

 th, Lecidea quemea usu. has a moi'e orange or brownish tint. 

 L. dubia, L. sporadiza, and varieties of L. parasema are usu. in 

 smaller patches. 



