BENEFICIAL ASSOCIATION AMONG PLANTS AND ANIMALS. 
By GeEorGE JAMES PEIRCE. 
For more than ten years the interest of biol- 
ogists has been held by those associations of 
animals and plants which seem to benefit both 
the parties concerned. About this, as about 
all important questions, there has been much 
difference of opinion, much argument, much 
ridicule. 
It is a matter of no small significance to bot- 
anists and zodlogists that organisms which, 
alone, would find it difficult to succeed in the 
struggle for existence, are able, by joining their 
efforts with those of other organisms of very 
different affinities, not only to survive, but also 
to attain a size and number far greater than 
their neighbors. 
To the late Anton De Bary, professor of bot- 
any at the University of Strasburg, we owe the 
introduction into the scientific vocabulary of 
the word syméiosis, which means ‘‘a living 
together.” He urged that it should be used in 
addition to, or in place of, the word Jarasitism. 
In all cases of parasitism one organism lives 
wholly at the expense of another. When it be- 
came evident to the scientific world that there 
are organic associations which are not in their 
nature parasitic, the word symbiosis was ap- 
plied to these beneficial unions only. Thus, 
just as the new field for investigation was 
opened, a name was ready for it. 
That there should be mutual benefit associa- _ 
tions among lowly aquatic organisms is indeed 
remarkable, but it is still more wonderful that 
the elaborately differentiated organisms of the 
land should combine into similar associations. 
The object of all these associations is to im- 
prove the chances of both organisms in the 
struggle for existence. The aquatic organisms 
are associated in order to secure better food 
supplies ; the land organisms combine for mu- 
tual protection against their enemies. 
Perhaps the most remarkable cases of symbi- 
osis, or beneficial parasitism, between animals 
and plants are afforded by certain ants and 
tropical trees. It is generally known that in 
the moist, fertile regions of the tropics, those 
plants whose leaves are tender and succulent 
are much more numerous than in temperate 
climes. Various devices are resorted to by the 
plants in order to protect their foliage; but of 
these devices the most noteworthy, and at the 
same time the most interesting, is the mainte- 
nance of a standing army of ants. 
Travelers tell us that it is not uncommon in 
the tropics to see a double line of ants stretch- 
ing from their hill, across an open space, and 
up some tree trunk. One-half the ants are 
toiling homeward under heavy burdens of leaf 
fragments ; the other half are hurrying toward 
the source of supply. 
The ants make a two-fold use of the leaves ; 
they eat the soft, green parts; they use the 
harder, woody parts, the veins and stalks, as. 
the supporting columns of their hills. From 
such systematic labor more or less complete: 
defoliation of the tree results. Against these 
marauders, therefore, some defense must be 
provided, and to this end certain plants are 
furnished with the means to attract, to hold 
and to impel honey-eating ants to fight for 
them. ; 
In tropical America there grows the tall, 
somewhat palm-like tree, called by the natives 
the /uzbauba, and known to botanists as Cecro- 
pia adenopus. It is rather slender; its holiow 
stem, divided like the bamboo into chambers. 
or joints, is crowned with large, tender leaves, 
which are very attractive to caterpillars and to: 
leaf-cutting ants. The contour of the hollow 
stem is smooth and even, except that, just be- 
low each joint in the outer surface of the stem, 
there is a depression which corresponds with a 
similar depression of the inner surface. A thin 
place is thus formed ; so each chamber is sep- 
arated from the outside world by a wall that is 
thin only in one spot. Through the thin place 
friendly ants bore readily, and soon find them- 
selves in a cavity of considerable size. Within 
this chamber they establish a colony. The 
house grows with the number of its occupants, 
so that the whole colony is never obliged to 
