. Bulletin. 1901-13. Agriculture; Agriculture. EFFECT UPON THE HOST. 19 killed by freezing, or otherwise being mechanically destroyed. It is maintained that in extreme cold weather mistletoe has been largely killed out over large areas; for example, in the unprecedented cold wave of February, 1900. Its own bulkiness and brittleness would seem to operate toward the self-destruction of the mistletoe bush. In the case of infection upon the mesquite, spoken of elsewhere, the parasite so injures the branch upon which it sits as to kill the branch and thereby destroy itself. Usually, however, accide
. Bulletin. 1901-13. Agriculture; Agriculture. EFFECT UPON THE HOST. 19 killed by freezing, or otherwise being mechanically destroyed. It is maintained that in extreme cold weather mistletoe has been largely killed out over large areas; for example, in the unprecedented cold wave of February, 1900. Its own bulkiness and brittleness would seem to operate toward the self-destruction of the mistletoe bush. In the case of infection upon the mesquite, spoken of elsewhere, the parasite so injures the branch upon which it sits as to kill the branch and thereby destroy itself. Usually, however, accident to the aerial part of the parasite merely results in stimulating the development of adventitious buds—and thereby in nmltiplying the number of mistletoe shoots upon a gradually widening area of infection. EFFECT UPON THE HOST. Perhaps in the majority of cases the original point of infection is upon a small, re- mote branch. The habit of the mistletoe is of course to draw sustenance from the branch and in increasing quantity as the parasite in- creases in size. The imme- diate result is to starve that portion of the branch lying beyond the point of infec- tion, and while this part may persist for some years alive without noticeable growth, in the end it dies, and the mis- tletoe thus comes to occupy the end of the branch. (See fig. 5.) This habit is particu- larly well shown in the water oak, where very large clusters 2 to 3 feet in diameter swing from the end of a long slender branch not more than an inch in diameter next the swollen point of junction of the host and parasite (PI. II, fig. 1). At the point of attachment also the branch is stimulated to excessive growth, which gives rise to deformi- ties of varying shapes on different host species. In the water oak just mentioned both branch and mistletoe are enlarged like a clumsy piece of welding. Frequently, as in the Osage orange, the })ranch is stijuulated to an excessive formation of shoots, forming a sort of witches'
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