124 ANIMAL INDIVIDUALITY [CH. 



are found free-living in spots less exposed than those 

 where lichens grow: the alga, that is to say, can 

 exist separately, but in the partnership grows more 

 luxuriantly and has a wider range. The fungus, on 

 the other hand, though it has been grown separately 

 in an artificial medium, cannot develop in nature 

 unless it meets with some algal cells. Fig. 12 shows 

 a young fungus which has just germinated among a 

 group of algae and is now sending forth little tentacles 

 to seize and enwrap them. 



The fungus gains more than the alga, but this 

 does not prevent the combination of both, the lichen, 

 from being a very definite individual. A lichen on 

 a barren rock is a something whose continuance 

 as such and in such a situation is dependent upon 

 the co-operation of its two constituents. Here the 

 division of labour is given beforehand in the two 

 kinds of plants, and the new individuality simply 

 arises from the fitting together of these two separate 

 beings into a very close and special relation. 



This relation is, however, only a special case of 

 the general relation existing in nature between green 

 plants and all other organisms. Put very crudely, 

 the relation is this : green plants can build up 

 protoplasm from water, carbon dioxide, and mineral 

 salts : the protoplasm thus formed is the ultimate 

 source of all nourishment to the rest of life. Animals 

 either eat green plants or else eat other animals 



