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 algae 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 algae 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 

 algae 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. - 

 FIG. 472. A crustaceous lichen To be strictly accurate, the 



(Graphis elegans) growing on holly : A, 



A 



natural size ; B, slightly magnified. 



two kinds of vegetable bodies 



