136 DISEASES OF TREES 



appearing on the leaves. Even with the naked eye one may 

 often recognize a grey covering on the diseased leaves. 



On more thorough investigation we perceive a luxuriant 

 mycelial growth in the tissues of the diseased parts, from which 

 innumerable short gonidiophores grow outwards. These pro- 

 duce tufts of long curved multicellular gonidia, which germinate 

 in moist air even in a few hours, and push their germ-tube 

 directly into the epidermis of the maple-leaves, which conse- 

 quently become brown. 



The mycelium, which is intercellular, swells up to form 

 large brown mycelial resting-cells and cell-plexuses, which 

 contain oil-drops. These persist during the winter, and carry the 

 disease over to the following year. The fungus is also able to 

 live saprophytically on humus in the soil. 



PESTALOZZIA HARTIGII l 



The disease induced by this fungus, which has often been met 

 with all over Germany, appears most frequently in seed- and 

 plant-beds which are stocked with spruces and silver firs. I 

 described it in the Allgemeine Forst- und Jagd-Zeitung, 1883, 

 where I advanced the view that it was due to the formation 

 of ice and the consequent crushing of the cambium. As I 

 expressly stated, the truth of the hypothesis which I there 

 advanced had still to be determined. Von Tubeuf has now 

 proved that here, as in so many cases, we have to do with a 

 parasitic disease. In summer one notices in nurseries of the 

 spruce and silver fir that a number of plants first become pale 

 and then die. If the plants are pulled up, it is seen that the 

 cortex on the parts immediately over the ground is withered, 

 but that, farther up, the stem is swollen as a natural consequence 

 of continued growth (Fig. 76). 



When the wood dries up or dies at the point where death of the 

 cortex first took place, the plant must perish. On the rind, at the 

 place where contraction is visible, one finds the mycelium of the 

 fungus, and numerous gonidial cushions which develop partly in 



1 C. v. Tubeuf, Beitrdge zur Kenntniss der Baumkrankheiten, pp. 40 51, 

 Plate V. Berlin, Springer. 1888. 



