1893.] Symbiosis and Mutualism. 519 
fected. Much research is needed in this matter. The manner 
in which the parasite acts and the host takes advantage of its 
work are not known with any certainty. 
To these probabilities, Frank adds certain characteristic 
improbabilities. One has already been spoken of, namely, 
that the plant develops tubes or hyphee for the purpose of self- 
infection which it sends through its tissues. This is somewhat 
like the algæ in some lichens which grow up among the asci 
in the sporocarp and are ejected with the spores. Only the 
latter is an established fact, the former a feat of the imagina- 
tion. Another of his ideas, pronounced a “settled fact” by 
Schneider in the article cited, is that “at the close of vegeta- 
tion and on other special occasions, the plant reabsorbs the 
protoplasm of the fungi.” After all the trouble of self-infec- 
tion to which the host has been, this seems rather like killing 
the hen that laid the golden egg. There is no sufficient evi- 
dence to establish so remarkable a phenomenon. Finally, 
Frank thinks that the roots of the Legwminose possess the 
power of attracting Rhizobia, due, as he considers, to some 
secretion. This is too much for his followers, and I think all 
will agree that it is the last straw of an unsupportable load 
with which he has already burdened our credulity. The 
exuberance of Frank’s enthusiasm, however, should not blind 
us to the fact that some relation of mutualism between the 
Leguminose and the tubercle parasites probably—almost cer- 
tainly—does exist. 
It is not necessary, as Frank seems to think, in order to 
establish mutualism to show that the organisms do no injury 
to each other. Mutualism of the kind we meet with in the 
vegetable kingdom involves sacrifices on the part of the host. 
The parasite is not there gratuitously. It is there to steal from 
its host the living it is hereditarily and constitutionally indis- 
posed to make for itself. If the host gains any advantage from 
the relation, it can only do so by sacrificing—by giving the para- 
site the benefit of its labor that it may subsist. If the plant or 
the plant colony benefits as a whole, it purchases the benefit by 
the sacrifice of certain parts or individuals. Mr. Webber, ina 
note on the Yucca moth in the American Natura ist for Sep- 
