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 stellarts (Ach.) typica et var. tenella, Scop. 
Sterilis. 
4. Physcia obscura (Ehrh.), var sorediosa. Sterilis. 
5. Physcia pulverulenta, var. pityrea (Ach.).  Sterilis. 
6. Lecanora (Squamaria) saxicola (Poll.). Rara. 
7. Lecanora (Placodium) murorum (Hffm.), Ach., Nyl. L. 
Paris. 119. Fertilis. K-+. 
Var. corticicola. Forma thallo contracto. K+. 
8. Lecanora (Placodium) callopisma, 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, K—, L. citrina, K+. 
10. Lecanora (Placodium) teicholyta, Ach. Raro fertilis. 
11. Lecanora candelaria, Ach., Nyl. Syn. i. 412; Lich. 
Scand. 108 (Physcia). K—.. Sterilis. 
A speciebus analogis Physcie longe differt reactione chryso- 
phanica nulla. 
12. Lecanora medians, Nyl. in Bull. Soc. Bot. de Fy. t. ix. 
1862, p. 262, sub Placodio. Haud raro fertilis. 
K-—. Distat itaque L. medians absolute ab extus sub- 
simili ZL. murorum, sed aftinis est L. vitelline et precipue L. 
crenate Nyl. (crenulata, Whinb.). 
