196 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. LXiii. 



Notes on the Witches' Broom of Pinus Sylvestris. 

 By A. W. BoRTHWiCK, B.Sc. 



(Read 9tli March 1899.) 



Witches' brooms are bushy growths on trees which are 

 induced by parasitic fungi. The fungus has a stimulating 

 effect upon the growth, and as a result we find an exces- 

 sive development of buds and twigs. The form of a 

 witches' broom varies, the most common being the hang- 

 ing clustered masses to be seen on many broad-leaved trees. 

 The twigs in some cases are much elongated, in others 

 shortened, but they never live long, and it is their rapid 

 development and premature death which give rise to the 

 tangled crow's-nest-like structure. 



The characteristic features of a witches' broom are that, 

 without regard to the direction of the branch on which it 

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

 that the point of infection is conspicuous as the starting- 

 point of tha broom. Shadebeck even regards any twig 

 hypertrophy as a witches' broom. 



Most witches' brooms are caused by an necidium or an 

 exoascus. They occur very abundantly on many broad- 

 leaved trees, those of the cherry and birch being extremely 

 common and familiar objects. Among the conifers we 

 ■ find them also, though not of such general occurrence as 

 among the broad-leaved trees. Probably the most com- 

 monly known one is that induced by secidium elatinum, 

 on the silver fir; and, as far as I know, the least common 

 one is that on our own Scotch pine. In the " Zeitschrift," 

 edited by Dr. von Tubeuf, May 1898, p. 195, a photo- 

 graph and a short account is given of a witches' broom on 

 Weymouth's pine — Pinus strohiis. In " Schlich," vol. iv. 

 p. 395, it is stated that a witches' Ijroom occurs on pines, 

 but the fungus which causes it is as yet unknown. 



Professor H. Mayr, of Municli, found this broom on 

 pines in Japan ; and lie kindly informs mc, in reply to a 

 letter, that they are to be found here and there on spruce 

 firs and pines, and that he even got them on cryptomeria, 

 but they are exceedingly rare. 



