246 Dr. Nylander on Lichens in the Luxembourg Gardens. 



The garden of the Luxembourg, by reason of its more 

 favourable situation, is less destitute of lichens than any other 

 public walk in Paris. Consequently lichens constitute in some 

 degree a standard of the salubrity of the air, and a very 

 sensitive hygrometer. The sweet-chestnuts in the Observatory 

 avenue are especially remarkable for the numerous lichens 

 growing on their bark, and which are in such abundance as 

 generally can only be found at a considerable distance from a 

 town. We are thus authorized to assert that this portion of 

 the Luxembourg is the most healthy spot of all Paris. 



Diligence has rendered the list as perfect as possible ; but 

 it should be remarked that those portions of the garden from 

 which the public is excluded may possibly have furnished 

 some additions. 



The number of lichens enumerated is about forty ; they are 

 as follows : — 



1. Parmelia acetabulum (Neck.), Dub. Forma virescens 

 sterilis. 



2. Physcia parietina^ L. Frequentissime fertilis. And 

 also forma thallo virescente, and a var. sorediosa marginibus 

 thalli sterilis sorediosis. 



3. Physcia stellaris (Ach.) typica et var. tenella^ Scop. 

 Sterilis. 



4. Physcia obscura (Ehrh.), var sorediosa. Sterilis. 



5. Physcia pulverulenta^ Y2iX. pityrea {Kch..). Sterilis. 



6. Lecanora [Squamaria) saxicola (Poll.). Kara. 



7. Lecanora {Placodium) murorum (Hffm.), Ach., Nyl. L. 

 Paris. 119. Fertilis. Kh-. 



Var. corticicola. Forma thallo contracto. K + . 



8. Lecanora {Placodium) callojpisma^ Ach., Nyl. L. Paris. 36. 

 DifFert a L. murorum thallo ; sporis crassioribus et paraphy- 

 sibus apice clava minore. 



9. Lecanora citrina^ Ach., Nyl. L. Paris. 35. Sterilis. Like 

 L. epixantha^ Ach., but with different chemical reaction : L. 

 epixantha^ JL — jL. citrina^ K + . 



10. Lecanora {Placodium) teicholyta^ Ach. Earo fertilis. 



11. Lecanora candelaria^ Ach., Nyl. Syn. i. 412 ; Lich. 

 Scand. 108 {Physcia). K — . Sterilis. 



A speciebus analogis Physcice longe diifert reactione chryso- 

 phanica nulla. 



12. Lecanora medians^ Nyl* ^^ Bull. Soc. Bot. de Fr. t. ix. 

 1862, p. 262, sub Placodio. Haud raro fertilis. 



K — . Distat itaque L. medians absolute ab extus sub- 

 simili L. murorum^ sed affinis est L. vitellines et praecipue L. 

 crenatce Nyl. {crenulata, Whlnb,). 



