MITUALISM. 87 



individual. These, and other examples, will serve to illustrate 

 how we have in the lichen an organism with peculiarities \' 

 structure and of life, widely differing from those of either an 

 alua or a fungus. This unification of two living beings int., an 

 individual whole, I have designated " Individuation.' n 



In the case of the lichen-symbiosis, the chlorophyllous part 

 .nudists of minute algal cells, completfly enclosed in a ti~ 

 of fungus-hyphae, and the lichen lives as a ],erfeetly isolated 

 and independent plant. The case is, however, different when- 

 the fungus enters into parasitic relationship with the -reen 

 cells of a large plant. Union may then take place, so that the 

 fungus lives on. or inside its host, and removed from contact with 

 any other substratum. The fungus is, however, not in a portion 

 to convey any nourishment to its host, and in fact is absolutely 

 dependent on it for the organic substance and water nece<-ar\ 

 for growth, ^'here, however, the relationship is such that the 

 parasitic fungus is still in contact with son,,, other substratum. 

 then it may be assumed that, in spite of its parasitism, it 

 takes up nutriment from this source, and shares it with its 

 host. This, as has already been pointed out. is the stale of 

 things in the lichens, where the fungus completely envelopes 

 the small isolated al-ae. and must, as a condition of the -rowth 

 of the lichen, remain in direct contact with the substratum: 

 the fnn-us is believed to take from the substratum water and 

 inorganic food-material with which it supplies the al-ae. while 

 it receives in return plastic organic substance to be used in 

 its own growth. ( f course cases do occur amongst the lichen-. 

 where, in moist places, the al-a is not dependent on the tun-us. 

 or, on the other hand, when- the fun-iis ran itself take up 

 or-anie substance from its substratum. 



Another example of the case is the union of I'un-i \\iih 

 Qon-chlorophyllous plants which inhabit humus (e.g. .]/,///..//// 1. 

 Hen- the fungus takes up or-aiiic nourishment from the 

 substratum and supplies it to the hi-hei plant, which, in 



consequence of it- lack of chlorophyll, is directly dependent on 



the plastic oigani/.ed substance from the soil, supplied throii-h 



the agency of the fun-us. The latter, however, receives noiliin- 



in return; it requires nothin-. since its substratum ollefs it 

 the QiOSl favourable conditions for nutrition This form of 



' lii'lh iiln.i 



