THE LARCH CANKER 23 



found. Hartig noticed certain microdimensional differences 

 between the canker fungus and the type Peziza calycina, 

 and named the former Peziza Willkommii, but as these 

 differences are not constant this name may be dropped. 

 The syiionomy of the fungus is difficult, and is discussed in 

 a note at the end of Chapter IV. 



The most important contribution which Hartig made to 

 our knowledge of the disease was the result of his experi- 

 ments on artificial infection. Previous experiments of this 

 sort had been carried out by Fischer, a practical forester, 

 in 1877 ; he cut pieces of bark and phloem out of a canker 

 area and fitted them into suitably-shaped holes made in 

 healthy trees ; the latter became infected and ultimately 

 showed all the features of canker. This proved that the 

 canker was due to some transmissible cause, and was not 

 entirely the result of unsuitable growth-conditions, as seems 

 to have been generally supposed by English foresters even 

 as late as 1895 ! But it did not establish a connexion between 

 the disease and any one fungus, since a portion of infected 

 tissue cannot be regarded as a pure culture of any particular 

 parasite, and, as far as Fischer's experiments could testify, 

 the- Peziza might be a more or less constant concomitant of 

 the canker without being its cause. 



Hartig's experiments were of a more exact nature. He 

 grew small larches one metre high in pots and infected 

 them on September 29, 1879, with ascospores through small 

 wounds. The pots were left in the open till the beginning 

 of January, when they were placed in a room, and by the 

 middle of January disease, accompanied by death of the 

 bark, was noticed within a centimetre of the points of infec- 

 tion. By the middle of February normal fructifications 

 were formed. Investigations showed that the mycelium 

 had grown in October, but rested in November and Decem- 

 ber, All attempts at infection with uninjured trees failed, 

 and it was only found possible to inoculate trees through 

 wounds. On this rather slender evidence Hartig based his 

 theory that the fungus could not gain admission to trees 

 which were entirely uninjured. 



