212 CO-OPERATION OF PLANTS. 



smaller subterranean partner, which feeds it from the ground. 

 The number of plants having symbiotic relations of the kind 

 described is very large ; most of the Ericacece, including heathers, 

 rhododendron, and similar plants ; Coniferce, including firs of all 

 kinds ; Salicacec^^ including poplars, willows ; and all Cupuliferce, 

 like the oak, beech, etc. 



It is of great interest to note that the chief species of flowering 

 plants which are symbiotic are gregarious in character, and, like 

 the oak, fir, and heather, form large forests or moors, and one is 

 filled with wonder at the magnitude of the immense colonies of 

 subterranean fungi which must exist, interlacing themselves at the 

 roots of such forests of trees. 



It will also be plain why there is such a profusion of fungi of 

 all kinds in forests around the roots of certain large trees. We 

 cannot yet state precisely the exact species of fungi which contract 

 union with these plants, or whether there is a selective affinity 

 between flowering tree and fungus. But this much is known — the 

 flowering plant, rather than be at a loss for a fungoid partner, will 

 unite with other fungi than it is usually connected with. 



Then again there are instances of certain trees living in sym- 

 biotic union with another plant, and at the same time beset by 

 animal and vegetable parasites. 



For instance, the common black poplar has its roots in symbi- 

 otic union with a fungus for purposes of nutrition. Then other 

 parts of the roots of the poplar will have the parasite toothwort 

 feeding on them ; again, on the upper branches of the same tree 

 may be found the mistletoe, whose presence on the poplar tree is 

 due to the bird, the missel thrush, which, through eating the berries 

 of the mistletoe, disseminates the seeds. The mistletoe, in turn, 

 will have lichens attached to it. 



In all, I suppose the poplar tree has nearly fifty plants or 

 animals living in symbiotic or parasitic association with it. 



I now come to the second part of my paper, namely, the co- 

 operation or symbiosis of algae with fungi. Almost the first place, 

 if not the most interesting one, in symbiotic communities, ought 

 to be assigned to the lichens, to which, as will be well known, the 

 Iceland moss and the litmus plant belong. These organisms, the 

 lichens, which were once classed as separate plants, are now 

 acknowledged to be of a composite character. 



