53o 



The Museum Gazette 



having been once affected, there was nothing to bring them 

 again under restraint. Each one of the associated twigs con- 

 tinued to grow and to branch out on its own account. No 

 one could take precedence of the rest, and hence the besom- 

 like formation which we see. We have again a good instance 

 of what Nature affords us so many, the persistence and steady 

 aggravation of consequences long after the originating cause 

 has ceased to exist. That initial cause was in almost all these 

 instances the attack of some parasite. The first effect of the 

 irritation, whether of a living grub, a fungal growth, or the 

 repeated punctures of some insect, was to attract sap and 

 stimulate premature and excessive growth, Ubi irritatio ibi 

 fluxus, as the doctors have it. The influence of the first stimu- 

 lation, might soon come to an end, and then the spoiled branch 

 would be left to develop as best it could. It must be under- 

 stood that no fresh attacks of the parasite would be necessary, 

 and that possibly neither insect nor fungus would remain 

 permanently in the tuft of twigs. To ascertain and identify 

 the exciting cause, the attacked bud must be examined very 

 early, for subsequently all trace of it may be lost. 



Having realised that an early stage is a tuft of small 

 twigs, we have next to note that these may remain separate 

 at their bases or may unite together. Whether the one 

 or the other occurs will depend upon details as to the posi- 

 tion and stage of growth of the bud attacked. The difference 

 in result may be that in the one case a hard wood-core 

 will be formed in the middle of the broom which may be 

 absent in the other. Although it is probable that in most 

 instances a bud is the part attacked, the state of our 

 knowledge by no means justifies the conclusion that such 

 outgrowths may not sometimes result from the irritation of 

 young and delicate bark. In such bark there exist many 

 latent embryo buds. It is even possible that in rare instances 

 the irritation may have been from mechanical injury and 

 not from the presence of any parasite. All the more 

 characteristic forms of the " broom " must, however, be re- 



