132 SYMBIOSIS 



" moral," reciprocal and healthy life of organisms. Shall 

 we for ever continue to interpret Nature in terms of the chaotic, 

 the diabolical and abnormal rather than in terms of the indus- 

 trious, moral and normal relations of life ? If one organism 

 exploits another without any counter-service, this is Parasitism 

 the definition is clear and unequivocal. As a result of such 

 exploitation there is ultimately weakness and loss of viability 

 on both sides, and the biological community, too, is a loser 

 thereby. If a relation long held to be parasitical, on closer 

 examination is yet discovered to exhibit an appreciable amount 

 of counter-service and of avail towards life, such relation should 

 pro tanto, if not altogether, be considered as symbiotic. The 

 wisest course will be to give a suspect species the benefit of a 

 doubt. Prof. Farmer takes the view that the widespread and 

 important relations between fungi and the roots of flowering 

 plants, for instance, represent a " not very one-sided parasitism. '" 

 In my opinion the relation constitutes, on the contrary, a case 

 of Symbiosis, though partially marred by abuse, by the recurrence 

 of depredation. Inasmuch as the relation is thus marred, there 

 is failure of permanence. The same botanist tells us that this 

 association of the root with a fungus is a very intimate one in a 

 large number of instances, and that it occurs in a very great 

 number of plants which would never be suspected of parasitic 

 habits. 



Obviously the general character of the plants concerned is 

 too high to warrant a sweeping indictment. The further facts, 

 communicated by the same author, may be said to speak for 



themselves : 



i 



The roots of many of our forest trees produce few or no root-hairs. 

 Instead of this they are closely invested with a hairy coating of fungal 

 hyphae. Not only do these hyphae ramify in the soil, but they also enter 

 the root itself. Sometimes, as in the pines, they only pass between the 

 cells, and do not enter them, but in other cases, as for example, in orchids 

 generally, they pierce the cell walls and enter the living cells. In both 

 of these types of mycorhiza the fungus is doubtless attracted to the root 

 by substances which have a food value for its hyphae, just as parasitic 

 fungi are induced to enter the bodies of their victims. But in a mycorhizal 

 association the cells of the root control the degree of Evasiveness which the 

 fungus can manifest, and not only so, but they often proceed to actually 

 digest the fungus itself after it has flourished within them, and at their 

 expense for a while. We have here, then, a beautiful example of two- 

 sided parasitism, in which the final balance of profit very clearly lies with 

 the flowering plant. It is practically certain that the fungus obtains 



