Bonnier has drawn attention to the fact that the mistletoe in its turn, remaining green in the winter, contributes food material to its host when the latter has lost its leaves.
Bonnier and one of his colleagues, Claude Roberjot, were killed.
Bonnier showed that the same relationship could be proved in the cases of such plants as the rattle (RhinanThus), the eye-bright (Euphrasia), and other members of the Natural Orders, Scrophulariaceae and Santalaceae, which effect a union between their roots and the roots of other plants growing near them.
For the complicated parasitism of isopods and Sacculinidae on the same hosts Giard and Bonnier (Bopyriens, 1887, p. 197) should be consulted.