332 PRACTICAL COURSE IN BOTANY 
382. Slavery, or partnership? — Now, what can be the 
object of this peculiar association? Is it a symbiosis, or 
a case of enslavement? The fungi, as we know, are all 
parasites, unable to manufacture their own food or to exist 
at all except at the expense of other organisms, living or dead. 
But the lichens have refined upon the gross rapacity of their 
order, and instead of indiscriminately destroying the hosts 
that furnish their nourishment, have used their victims to 
better purpose by converting them into contented, well-fed 
slaves! The imprisoned alge perform for them the same 
service that the chlorophyll bodies do for the higher plants, 
and so the lichen fungi have the advantage of other parasites 
in getting their food manufactured at home, so to speak. 
And while the alge have to do double work in order to feed 
both themselves and their masters, the fungus, in return, 
shelters them against cold and drought, and prolongs their 
growing period by giving them a more continuous supply 
of moisture and food materi- 
als, which it draws from the 
substratum by means of its 
rhizoids. In this way both 
plants are enabled to live in 
situations that neither could 
occupy without the other. 
383. Reproduction.— The 
multiplication of the lichen 
alge is exclusively vegetative. 
The fungus, on the other 
hand, reproduces normally 
by spores, and the fruiting 
bodies found on the thallus 
originate from the fungus 
mycelium. 
384. Classification. — 
Fic. 472.—A_ crustaceous lichen To be strictly accurate, the 
(Graphis elegans) growing on holly: A, é : 
natural size; B, slightly magnified. two kinds of vegetable bodies 
