50 



fungous diseases that affect our crops, — less spectaciilai' in tlieir 

 working, but none the less damaging in their effects? Or is it 

 that well recognized factors are here found in a unique combina- 

 tion tliat adds to the seriousuess of Ihe situation? Is this dis- 

 ease inherently nu)re serious than pear blight or cotton wilt or 

 wheat stem rust? Answers to snch qnestions involve considera- 

 tiou of the liabils aud value of tlie liosi ])hiiil, as well as definite 

 knowledge on all important points in the life iiistory of the causa- 

 tive organism, Diaporthe parasitica. 



For chestnut bark disease infectiou to occur, tliree general con- 

 ditions must be met just as for au}^ other fungous disease. 

 Uroadly stated, these are (1) the presence of infective material, 

 (2) a host plant in a condition of susceptibility, (3) general en- 

 vironmental conditions that are favorable. All rational control 

 measures for the disease must be based on the peculiarities of this 

 fungus Avith reference to these three things. 



The infective material for Diaporthe parasitica seems to be 

 jM-e-eminently the spores, which are of two types, the pycnospores, 

 s(uu('tinies called conidia or summer spores, and the ascospores, 

 or winter spores. AVe wish to know definitely the conditions that 

 influence the formation of each type, the longevity of each under 

 favorable and under unfavorable conditions, their modes of shed- 

 ding and of transfer, the conditions favorable and unfavorable to 

 tlieir germination, their abilities to establish the fungus upon 

 various lualei-ials, aud the relative; iiuportance of the two types 

 ill sj)reading the disease. General cuviroiunculal conditions may 

 have their effect upon longevity of sj»ores, upou germiiuition of 

 spores, upon rapidity of gro^Ath of the fungus, and upon spore 

 production by the fungus. Susceptibility in the host has refer- 

 ence to qualities of genera or species or varieties or strains or 

 iiulividuals, that render them liable to attack by the fungus, 

 which qualities may be inherent or possibly induced by environ- 

 mental conditions. Here must be included the exposure through 

 various wounds of susceptible portions of the host; and the pro- 

 tective effects of measures that may lessen the susceptibility of 

 the host. Other points in the general life histor}' of the organism 

 may l)e of interest and importance, aside from any direct rela- 

 tion to the setting up of infection. 



