Diseases of plants induced by Diseases of plants induced by cryptogamuc parasites; introduction to the study of pathogenic fungi, slime-fungi, bacteria, and algae. English ed. by William G. Smith diseasesofplants00tubeuoft Year: 1897 MUTUALISM. 89 the case of the so-called ' stonn-tirs' of the mouutains, on which are developed not a single apex, as in the normal fir, but many, each of which grows up like a little independent tree on the branches of the old stem. A similar result follows where a porticjn of a lateral l)ranch is planted as a ' cutting,' one bud grows directly upwards, the othe
Diseases of plants induced by Diseases of plants induced by cryptogamuc parasites; introduction to the study of pathogenic fungi, slime-fungi, bacteria, and algae. English ed. by William G. Smith diseasesofplants00tubeuoft Year: 1897 MUTUALISM. 89 the case of the so-called ' stonn-tirs' of the mouutains, on which are developed not a single apex, as in the normal fir, but many, each of which grows up like a little independent tree on the branches of the old stem. A similar result follows where a porticjn of a lateral l)ranch is planted as a ' cutting,' one bud grows directly upwards, the others form lateral branches. The stimulating effect which the removal of the terminal shoot produces on lateral branches is thus one which extends to a considerable distance. A stimulus of a somewhat similar nature appears to be exerted on buds attacked by certain fungi, so Kio. 111.—Witches' broom of Silver Fir, caused by AicUUam elatinitm. (v. Tuteiif phot.) that the sliDOt produced from such a bud no longer retains its normal direction of growth, Itut becomes negatively geotropic, like an independent plant. This marked negative geotropism is characteristic of all witches' l)rooms (Fig. 16), and shows clearly that they are no longer controlled by the same laws of grcnvth as the n(jrmal lateral branches. They have in addition other peculiarities not e\hil)ited l)y normal plants. Thus tlie witches' broom of the silver Hr causetl by iiiyccliiini ot Aa-uliuni di(tiiiiiiii is not evergreen, but bears needles whieh fall each autumn. Moreover, no witches' broom Itears (lowers or I'liiit; for example, that on the cherry (Fig. 5) ]) exclusively leaf-buds which unfnjil siiiiultaneousjy with ttie
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