Diseases of plants induced by Diseases of plants induced by cryptogamic parasites; introduction to the study of pathogenic Fungi, slime-Fungi, bacteria, & Algae diseasesofplant00tube Year: 1897 MUTUALISM. 89 the case of the so-called ' storni-tirs' of the mountains, on which are developed not a single apex, as in the normal lir, 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 portion of a lateral branch is planted as a ' cutting,' one bud grows directly upwards, the others form lateral branches. The stimulating
Diseases of plants induced by Diseases of plants induced by cryptogamic parasites; introduction to the study of pathogenic Fungi, slime-Fungi, bacteria, & Algae diseasesofplant00tube Year: 1897 MUTUALISM. 89 the case of the so-called ' storni-tirs' of the mountains, on which are developed not a single apex, as in the normal lir, 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 portion of a lateral branch 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 wdiich extends to a considerable distance. A stimulus of a somewhat similar nature appears to be exerted on buds attacked by certain fungi, so I-'lf;. 1,;.—Witches' Ijroom of Silver Fir, caused by Atcidiuiii datinam. (V. Tubeuf phot.) that the shoot produced from such a bud no longer retains its normal direction of growth, but becomes negatively geotropic like an independent plant. This marked negative geotropism is characteristic of all witches' brooms (Fig. 16), and shows clearly that they are no longer controlled by the same laws of growth as the normal lateral branches. They have in addition other peculiarities not exhibited by normal plants. Thus the witches' broom of the silver fir caused by mycelium of AecicUum datinum is not evergreen, but bears needles which fall each autumn. Moreover, no witches' broom bears flowers or fruit ; for example, that on the cherry (Fig. 5) produces exclusively leaf-buds, which unfold simultaneously with the
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