88 DISEASES OF TREES 



we meet with the most varied forms of gonidia, which are pro- 

 duced either free on the stroma, or in the interior of cavities in 

 the stroma, or in pycnida. Owing to the ease with which all 

 these organs of reproduction germinate, the parasite is frequently 

 very abundant. 



In a similar manner, C. Sorbi appears to attack the bark of 

 Sorbus Aucuparia. 



Here allusion may be made in a few words to the " Disease- 

 blotches" on the leaves of numerous trees, shrubs, and herbs. 

 These often occur in great abundance in autumn, the leaves being 

 covered by numerous sharply defined blotches, which are usually 

 circular in outline and brown in colour, and frequently surrounded 

 by a red margin. They are generally due to fungi belonging to 

 the family Sphczrelloidea, and especially to the genera Sphcerella 

 and Stigmatea. 



The gonidia are formed on the living leaves, but the perithecia 

 only on the dead parts of plants, and usually not until the spring 

 after the leaves have fallen. 



Sphczrella Fragarics produces the diseased blotches on the 

 strawberry. 



.S*. punctiformis and >S. maculiformis produce brown blotches 

 on the leaves of the oak, lime, and hazel. 



5. Fagi produces blotches on the leaves of the beech, &c. 



Stigmatea Mespili induces brownness in the leaves of the pear. 



Stigmatea Alni is the cause of blotches on the leaves of the 

 alder. 



Gnomonia belongs to an allied family, Gnomonia erythrostoma , 

 producing a brown colour in the leaves of the cherry. The in- 

 fected leaves die prematurely, but do not fall off. On these are 

 developed the perithecia with their unicellular tubular spores. It 

 is advisable to remove during winter all leaves that may be 

 hanging on the trees. 



A parasite, Valsa Prunastri, frequently proves injurious to the 

 apricot, cherry, and sloe. The fungus infests the cortex, and 

 causes the death of the branches. . The form producing spermatia 

 is the first to appear, and ejects its tendril-like masses of sper- 

 matia ; while later namely, in the following spring the peri- 

 thecia develop in the dead cortex. 



