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 THE PARASITIC EXOASCEAE. 159 ducing the brooms by artificial infection of alder. The disease is common and epidemic, and a single tree may carry as many as a hundred brooms. The witches' brooms are composed of many thickened twigs, beset with an abnor- mal number of lenticels, and the point of infection shows a distinct swelling, from which the broom tends to turn directly upwards. The leaves are some
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 THE PARASITIC EXOASCEAE. 159 ducing the brooms by artificial infection of alder. The disease is common and epidemic, and a single tree may carry as many as a hundred brooms. The witches' brooms are composed of many thickened twigs, beset with an abnor- mal number of lenticels, and the point of infection shows a distinct swelling, from which the broom tends to turn directly upwards. The leaves are somewhat modified, they are larger and thicker than the normal, they unfold later and wither earlier, while their stipules remain attached for some time. The brooms of alder only survive a few years, and by their decay cause the death of large branches, and frequently of the whole tree. The asci, which are sunk in a depression of their stalk-cell, form a white coating on both surfaces of the leaves. The mycelium hibernates in the buds. Exoascus turgidus Sad. causes the formation of witches' brooms on Bet via verrucosa. The leaves form- ed on the brooms are some- what crumpled, and the asci are produced on their lower surface. Exoascus betulinus Eostr. produces witches' brooms on Betula puhescens and B. odorata. Fig. 54.—Exoascus epiphyllus. Witches' broom in first year, showing swelling at the point of infec- tion. The leaves are already shed in autumn, while the normal still remain 1 natural .size. After V. Tubeuf.)
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