AY. N. C. Bklgravk L93 



The recent work of Shear (3) and Harper (2) has indicated the 

 existence of "strains" within the same species of fungus which behave 

 differently in culture media. It seems probable that the fungi here 

 investigated were conidial bearing strains only. The constant cultural 

 differences described above point to the existence of different strains. 



Inoculation experiments. 



These have, so far, yielded negative results. A T-shaped cut was 

 made in the bark of a healthy plum shoot, and a small piece of 

 mycelium introduced under the edges of the cut. 



Inoculations made in September, 1913, were examined a year later 

 but no signs of infection could be found. 



In view of the negative results yielded by the infection experiments 

 up to the time of writing conclusive proof that the "die-back" disease 

 under investigation is caused by the fungi in question is lacking. There 

 is however strong presumptive evidence that they are responsible. 

 Their presence in the tissues of the host in each case examined, the 

 general character of the development of their fructifications on the 

 diseased bark, the identity with or close relationship to Cytospora 

 leucostoma, a parasitic fungus known to cause a strikingly similar 

 disease on cherry trees, of the fungus isolated from the diseased areas 

 of the affected plum trees in most cases examined, and the failure to 

 find in the diseased parts any other organism to which the disease could 

 be attributed, are points which, taken collectively, suggest that the 

 fungi in question have caused the trouble. The lack of confirmative 

 evidence from the infection experiments, although rendering absolute 

 proof of the cause of the disease at this stage impossible, does not 

 necessarily conflict with the view that these fungi are the cause, since 

 it is always possible that the conditions necessary for successful infection 

 did not obtain in the experiments already conducted. 



Ann. Biol, ir 13 



