ENTIRE LEAVES AFFECTED BY FUNGI. 



523 



time the patch becomes a sunken, blistered hole from which resin flows; and every 

 year the fructifications appear above the cortex in the form of numerous little 

 cup-like structures which are white outside and scarlet-red in the concavity. As 

 the disease progresses the infected patch gradually spreads, and infected trunks and 

 branches can be easily distinguished at a distance. Towards the end of summer 

 the needles on the twigs above the canker turn yellow, while those on the healthy 

 branches are still a beautiful green. This premature discoloration is a sure sign 

 of the speedy death of the whole bough. A similar canker is produced on the 



Fig. 358.-Various Galls. 



1 Gall on the bract-scales of the pistillate flowers of the Gray Alder (Alnus incana) produced by Exoascus Alni-incance. 

 2 Inflorescence of Valerianella carinata. * The same inflorescence with galls produced by a gall-mite. Leaf rosette of 

 the House-leek (Semperoivum hirtum). Leaf rosette of the same plant which has been attacked by the fungus Endo- 

 phyllum Sempervivi and has become hypertrophied. 



Silver Fir (Abies pectinata) by ^Ecidium elatinum, but instead of being only on 

 one side of the branch, as in the Larch, it forms a uniform swelling all round it. 

 Cankers of this kind are produced by a Bacterial organism (Bacillus amylovorus) 

 on fruit-trees (Apple, Pear, &c.), and on various trees belonging to the Amentiferae 

 (Beeches, Hornbeams, Oaks, &c.) by the Fungus Nectria ditissima. 



When whole leaves undergo hypertrophy of the kind we have particularly 

 remarkable changes of form. For example, the normal leaves forming the rosettes 

 of the House-leek (Sempervivum hirtum; see fig. 358 4 ) are broadly obovate in 

 form, being little more than twice as long as they are broad. The leaves of the 

 same plant after they have been attacked by the parasitic Endophyllum Semper- 



