Dr. Nylander on Lichens in the Luxembourg Gardens. 245 
XXVII.—Notule Lichenologice. No. XXIII. 
By the Rev. W. A. Leicuton, B.A., F.L.S. 
Dr. NYLANDER has published, in the ‘ Bulletin of the Botanical 
Society of France’ (t. xii. pp. 364 &e.), a very interesting 
account of the lichens which he collected in the garden of the 
Luxembourg Palace at Paris. Independently of the valuable 
lichenological information it comprises, it 1s an instructive 
example of what diligent and accurate research may accom- 
plish in a circumscribed space, and a proof that botanists need 
not go far afield for their collections, but that treasures lie at 
their very doors, if only their eyes and hearts will look for and 
appreciate them. 
The paper is prefaced by some remarks which, excellent in 
themselves, are also highly suggestive in various ways. Of 
all plants, lichens are the most extensively diffused, living on 
barks, woods, rocks, stones, and earth, especially when these 
substrata are located in a pure fresh air, which is absolutely 
essential to their nourishment and healthy development. Most 
lichens, as a general rule, avoid towns, and if they make their 
appearance there, are most frequently found in a state of in- 
complete development, either sorediate or entirely sterile. 
There are, indeed, some few species (as Physcia parietina, Ph. 
pulverulenta, var. pityrea, Ph. obscura, Ph. stellaris, Placodium 
murorum, Pl. callopismum, &c.) which willingly inhabit cul- 
tivated places; but in the interior of great towns we may ge- 
nerally search in vain for them on the trunks of trees and on 
the walls. In such localities their usual abodes are occupied 
by Cryptogams of an inferior order (such as Protococcus), which 
delight especially in an impure air, or one surrounded with 
houses or walls. Lichens, on the contrary, refuse to live in 
such conditions. The trunks of trees in the gardens and 
plantations of great towns are for these reasons destitute of all 
trace of lichens. On the other hand, in the open country 
every tree is more or less adorned with thalli and apothecia of 
divers colours. The magnificent trees of the gardens of the 
Tuileries bear scarcely anything but Protococcus. In the 
Jardin des Plantes scarcely any trees bear lichens, and those 
only in the most exposed places. 
We may observe, en passant, that lichens are by no means 
parasites, properly so called; and it is at least very doubtful 
whether they are injurious to the trees upon which they grow. 
All that can be said is that they may to a certain extent be 
injurious to the living bark, either by obstructing its respira- 
tory functions or by applying to its surface an excessive 
humidity. 
