268 THE VEGETABLE WORLD. 
The Orchil or Archil is a valuable die, and Lecidea Tartarea 
is the cudbear of commerce, which is imported to the value of 
£80,000 annually. 
One of the most curious of this family of Thallogens is Lecanora — 
esculenta, a lichen which is frequently met with in the mountaims 
of the arid deserts of Tartary. It is found in great abundance m 
the Kirguis deserts to the south of the river Jaik. It seems t 
fall from the sky as a sort of miraculous manna. Men and beasts 
are nourished on it. But what is really remarkable is that it 
occurs in the form of -small globules, whose size may vary from the 
head of a pin to a hazel-nut. They are invariably free, being 
attached to no other body. It follows from all this that the Lichen 
develops itself rapidly ; has vegetated and increased while the = 
transported it from one place to another. The light mass whic 
constitutes these Lichens are, in short, often transported by the 
air to great distances. The manna which supported the Israelites 
tants eagerly profited by the occasion, and made it into b 3 
In stating this fact for your information, I would pray The 
analyse them, and favour me with your opinion upon ret tible 
grains enclosed in the letter were the grains of the come 
Lichen the Lecanora esculenta now under consideration. 
What then is the internal organisation of Lichens P 7 
These Thallogens, when perfect, consist of a nutritious pine 
tative apparatus designated the thallus, and of double reprodne® 
organs. 
A thallus, which is sometimes imperceptible, may acer 
attain the length of ten yards. The colours which it pais or 
presents are white, grey, yellow, citron, orange, BE: = ' 
black. As to its form, it is foliaceous in Parmelia; 
