268 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



remarkable phenomenon of heteroecism i.e. the 

 inhabiting more than one host of the fungi. De 

 Bary proved that the old idea of the farmer, that the 

 rust is very apt to appear on wheat growing in the 

 neighbourhood of barberry-bushes, was no fable ; but, 

 on the contrary, that the yellow <&Lcidium on the 

 barberry is a phrase in the life-history of fungus 

 causing the wheat-rust. Many other cases are now 

 known, e.g. the sEcidium abietinum^ on the spruce 

 firs in the Alps, passes the other part of its life on the 

 Rhododendrons of the same region. Another well- 

 known example is that of the fungus Gymno- 

 sporangium, which injures the wood of junipers : 

 Oersted first proved that the other part of its life is 

 spent on the leaves of certain Rosaceae, and his 

 discovery has been repeatedly confirmed. I have 

 myself observed the following confirmation of this. 

 The stems of the junipers so common in the 

 neighbourhood of Silverdale (near Morecambe Bay) 

 used to be distorted with Gymnosporangium, and 

 covered with the teleutospores of this fungus every 

 spring: in July all the hawthorn hedges in the 

 neighbourhood had their leaves covered with the 

 ./Ecidium form (formerly called Rcestelid), and it was 

 quite easy to show that the fungus on the hawthorn 

 leaves was produced by sowing the Gymnosporangium 



