TIIK I'AKASITir KXoAM 'KAK. 14") 



The presence i>t' ;i perennating mycelium is the cause oi 

 many .so-called "witches' brooms" on woody plants. In fact. 

 tin- majority of the structures known liy that name arc caused 

 by sjiccics of /y/v/.s,-//.s, though these ot' barberry, silver tir, 

 acacia, and buckthorn, are due to I'lvdim-ae. and others arc 

 ascribed to mites (7V/ ////</ //.s). 



'Witches' Jlroom.- " < lle\enbe-en ) arc bushy growth-, which 

 remind one at first sight of stranger-plants urou in-, like 

 mistletoe, on the branches of other plants. They generally 

 originate from a bud which has been infected during the previou- 

 -u miner, either directly or through its subtending leaf. This bud 

 produce's a twig capable of abnormally increased growth, most of 

 its sleeping buds are developed into branches, and the whole 

 system -hows marked negative geotropisni. (See Fig. 3). The 

 spores of the fungus are produced on the leaves of the broom. 



The characteristic features of a witches' broom are: that. 

 without regard to the direction of the branch on which it i> 

 borne, it is negatively geotropic in a marked degree, and 

 endeavours to develop like a terminal leader shoot : -that the 

 point of infection is di-tinctly conspicuous as the starting point 

 of the broom. Sadcbeek regards any twig-hypertrophy as .1 

 witches' broom, even that of Ei-un^n* T<>*inin<tii where then- 



is no basal swelling and the twigs exhibit only very slight 

 lie-alive -eotropism. 



The forms of witches' brooms are very varied. Among-t 

 the best known are the hanging broom-like masses developed 

 from buds of the leader shunts (,.//. on cherry trees). A- a 

 result of the rich -rowth of twigs and their premature death. 

 many of these brooms become tangled nest-like -tinctures. The 

 iwi-s in some are much elongated, in others shortened, in 

 very case, however, they arc abnormally numerous. As a rule 

 I he original leader shoot, on which sonic lateral bud has developed 

 into a witches' broom, shrivels up and dies, its contents being, 

 .1- it were, absorbed by the hypert rophicd brain-he.-. HI her 

 genera] features have already been di-<-u--cd in Part 1. of 



this book. 



Smith 1 found that the form of the witched broom i- not 

 determined exclusively liy the fungus. The pen-nnating m\ - 

 celiiini indeed givea I he tirst impetus towards it.- formation. 



1 Sniii li, {OC. fit. 

 K 



