COMRADES OF THE PLANT WORLD 
through chance proximity, without a conscious 
pact or deliberate contract. 
Edward Step in his illuminating book Mess- 
mates sums up the matter admirably: ‘Two 
friends in good health, each able to earn his 
own living, agree for the sake of companion- 
ship to live together, but each defraying the 
cost of his own necessities and luxuries. This 
is a case of mutualism. ‘Two other friends also 
agree to share quarters and have a common 
table; but one may be infirm and wealthy 
whilst the other is strong and comparatively 
poor. The infirm one offers to pay two-thirds 
of their common expenses if the other will con- 
tribute one third, plus his protection, cheerful 
companionship or other valuable help. This 
is a commensalism. The pair are messmates, 
each contributing to hotch-potch according to 
his ability or endowment, each affording what 
the other lacks, and both, therefore, benefitting 
from the partnership.” | 
It must be admitted that there are cases of 
plant companionship in which, to all human 
perception, the material benefits seem directly 
one-sided, but who can conclusively deny that 
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