138 DISEASES OF TREES 



spheroidal pycnidia, and partly on flat stromata which are 

 disposed in the tissue of the cortex. 



The characteristic gonidia (Fig. 77), which are situated on 

 short or long stalks, are at first hyaline, thin, oval, and uni- 

 cellular, but afterwards become four-celled owing to repeated 

 transverse division. The two middle cells are large and dark, 

 the small stalk-cell and the terminal cell remain colourless. The 

 latter pushes out a branched filament which, however, must not 

 be confounded with a germ-tube. It is only one or other of the 

 three lower cells that germinates, most frequently the lower of 

 the two brown middle cells. 



On account of the general distribution of this disease, and the 

 consequent loss incurred, it would appear advisable carefully to 

 root out and burn all diseased and dead plants that may be 

 found in nurseries. 



Similar pathological symptoms have also been observed on 

 young beeches, ashes, and maples. I should be glad to receive 

 such plants, in order to prove whether parasites are the cause of 

 disease, and, if so, to determine the species. 



PHOMA ABIETINA N.SP. THE FUNGUS OF THE CORTEX 

 OF THE SILVER FIR 



A disease which has not hitherto been described, but which is 

 extremely common on young and old trees in the Bavarian 

 Forest, is due to a parasite which may temporarily be called 

 Phoma abietina. The disease may be recognized by both small 

 and large branches of the silver fir becoming pale and withered ; 

 in fact, I have occasionally observed diseased spots two inches 

 in diameter on the cortex of silver firs as thick as one's arm. 

 As a rule the disease appears only on branches or on the main 

 axis of the younger classes of silver firs, and attracts atten- 

 tion by the cortex dying right round the branch, as is shown 

 in Fig. 78. 



Numerous small black pycnidia break through the epidermis 

 and appear on the dead cortex, either as small roundish bodies 

 or as many-chambered, irregularly shaped, black sclerotium-like 

 tubercles (Fig. 79, a). Numerous unicellular, colourless, abruptly 



