DISEASES OF TREES 



MELAMPSORA SALICINA. 1 THE WILLOW-RUST 



Several species of Melampsora occur on the various willows, 

 and these, until a short time ago, were grouped under the 

 common collective name of M. salicina. By means of the form 

 of the teleutospores and uredospores, Thiimen was the first to 

 distinguish a number of species, which ought to be thoroughly 

 investigated for the sake of verification. 

 Rostrup 2 has, in the interval, succeeded 

 in obtaining the aecidia of two species, 

 which will now be more particularly 

 described. 



MELAMPSORA HARTIGII 

 The uredospores appear sometimes as 

 early as the end of May or the begin- 

 ning of June, in small reddish yellow 

 clusters on the lower surface, more 

 rarely on the upper surface, of the 

 leaves of Salix pruinosa, S. dapJmoides, 

 S. viminalis, and other willows. The 

 disease spreads rapidly, partly owing to 

 the internal growth of the mycelium, 

 which penetrates the cortex of the 

 shoots by way of the leaf-petioles, and 

 partly by means of the uredospores 

 which are carried by the wind. These 

 germinate very quickly, and produce 

 numerous new uredo-clusters, generally 

 on the eighth day after they have been 

 sown on a sound leaf. Leaves that are 

 attacked soon become marked with black blotches, and drop off. 

 Before the leaves fall off or die numerous teleutospore-layers, 

 about the size of a pin-head, develop beneath the epidermis of 

 the leaf (Fig. 101). These occur more especially in late summer 



1 Von Thiimen, Mittheilungen aus dem forstlichen Versuchsuuesen Oester- 

 reichs y ii. p. 41 et seq. Hartig, Wichtige Krankheiten der Waldbdume^ 

 pp. 1 1 9 et seq. 



2 Rostrup, Fortsatte Undersogelser <n>er Snyltesvampes Angreb par 

 Skovtraeerne Kjobenhaven^ 1883. 



FIG. ioi. M. Hartigii on 

 Salix p)~uinosa. a, a living 

 leaf with sporophores ; ^, 

 a leaf which has been 

 killed at places ; c, sporo- 

 phores on the stem close 

 to the base of the leaf. 



