INJURIES INDUCED BY PLANTS 177 



because a sufficient supply of foliage is always left on the older 

 parts of the branches as well as on the youngest shoots. As the 

 meteorological conditions are not always equally favourable for 

 the germination of the sporidia, and as the teleutospores may 

 germinate at a time when most of the spruces are either too far, 

 or not far enough, advanced in development to be infected by 

 the sporidia, it very seldom happens that the disease maintains 

 its intensity throughout a long series of years. With the 

 exception of a spruce wood in the Saxon Erzgebirge, I have 

 never come across very serious damage due to Chrysomyxa 

 Abietis. Certain years occur, and not uncommonly, when the 

 disease is very scarce, and when the spruces are in a position to 

 clothe themselves with a full stock of leaves. On this account 

 I am not able to agree with Willkomm, Frank, &c., in their 

 recommendations regarding measures for combating the fungus, 

 because felling the diseased trees, and such like measures, would 

 have worse consequences than the disease itself. 



It may be not uninteresting to note that in the severe winter 

 1879-80 it was noticed that in many districts the diseased leaves 

 dried up so that the development of the fungus was prevented. 

 And, further, it not unfrequently happens that Hysterium macro- 

 sporum is encountered along with Chrysomyxa, the result being 

 that the development of the leaves is interfered with, and they 

 acquire black blotches. 



CHRYSOMYXA RHODODENDRI * 



The Rust of the Rhododendron is of special interest in that it 

 is hetercecious, developing its teleutospore- and uredo-layers in 

 clusters in the form of small roundish and oblong cushions 

 on the leaves of rhododendrons, while the aecidia (/Ecidium 

 abietinum, the Spruce-Blister-Rust) develop on the leaves of the 

 young shoots of the spruce. 



The occurrence of the disease on spruces is consequently 

 dependent on the presence of rhododendrons, 2 although, of 

 course, the spread of the sporidia, by means of wind and rain, 

 from high elevations into the valleys or otherwise is not im- 

 possible. De Bary, to whom we are indebted for our know- 



1 De Bary, Bot. Zeit., 1879. 



2 In the Alps R. hirsutum and R. ferruginium are the common species. 



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