1893.] Symbiosis and Mutualism. 509 
SYMBIOSIS AND MUTUALISM.:! 
By Roscor Pounp. 
Symbiosis and mutualism, in the vegetable kingdom at least, 
are phenomena accompanying parasitism. Parasites have 
various effects upon their hosts, according to the nature of the 
parasite, its mode of life and method of attack. In some cases 
the host is quickly killed and the parasite becomes a sort of 
saprophyte upon the remains. In others the host lives longer 
or is only partially affected. In still others the host lives on 
side by side with the parasite indefinitely. A further develop- 
ment is attained in cases where the parasite and host not only 
live together, but are mutually beneficial, and, perhaps, even, 
in extreme cases, inter-dependent. To the first phenomenon 
—namely, the living together of parasite and host—DeBary, 
in 1869, in a work entitled Die Erscheinung der Symbiose, gave 
the name of Symbiosis. The latter phenomenon—i. e., mutual 
assistance or inter-dependence of parasite and host—was named 
mutualism in 1873 by Van Beneden in his “Animal Parasites 
and Messmates.” Symbiosis in the strict sense and mutualism 
are often confounded, that is, the term symbiosis is often used 
to mean mutualism as such; but, in strictness, while mutual- 
ism, in the case of plants, can only exist with symbiosis, in the 
larger proportion of cases of symbiosis there is no mutualism. © 
At the outset it should be noted that the mutualism of which 
we are here speaking is mutualism of parasite and host—not 
mutualism of independent organisms. Of the latter, we have 
many examples in the animal kingdom, and, indeed, the 
human race furnishes examples of it. There is a sort of 
mutualism between man and wheat, for example. Wheat is 
cultivated by man and enabled to grow in quantities, and in 
localities which, under ordinary conditions, would be impos- 
sible. It gains this partial exemption from the struggle for 
existence only at the expense of an immense number of indi- 
1Read before the Botanical Seminar of the University of Nebraska, December 17, 
1892. : 
