526 



ALTERATION OF FORM BY PARASITIC FUNGI. 



farther apart than in the healthy plant on account of this stretching of the stem. 

 The lower leaves of the shoot are transformed into small fringed scales, and the 

 upper ones are so much shortened that their outline becomes almost circular. The 

 second parasite to which the Cowberry shoot is subject is Exobasidium Vaccinii (a 

 near ally of the already mentioned Exobasidium Lauri, p. 521). The stem becomes 

 pale rose-red colour, and rather thickened and spongy, but it does not elongate 

 much more than usual; the leaves become blistered and curiously convex on the 



Fig. 359. A Witches' Broom on the Silver Fir, produced by jEcidium elatinum. 



under surface. The substance of the infected leaves becomes brittle and loses its 

 chlorophyll. A red tint appears in place of the green, especially on the upper 

 surface of the leaf, whilst the lower surface, on which the spores develop, looks as if 

 it had been dusted over with flour. Usually the buds develop prematurely on these 

 shoots, i.e. the buds which, under ordinary circumstances, would not develop until 

 the next year push out and form new shoots shortly after they have been laid down. 

 The axes of these shoots, however, remain short; their leaves are closely crowded, 

 red in colour, and sessile. From a distance the premature shoots look like large 

 double red flowers inserted in the dark green of the non-infected Cowberry bush. 

 The shoots which develop prematurely on the shrubs of the Bog Whortleberry 

 (Vaccinium uliginosum) by the action of Exobasidium Vaccinii are often met 

 with in alpine regions, and are even more noticeable on account of their fiery-red 



