50 



fiiiigoiis diseases that affect our crops, — less spectacular in their 

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

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

 tion that adds to the seriousness of the situation? Is this dis- 

 ease inherently more serious than pear blight or cotton wilt or 

 wheat stem rust? Answers to such questions involve considera- 

 tion of the habits and value of the host plant, as well as definite 

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

 tive organism, DiaportJie parasitica. 



For chestnut bark disease infection to occur, three general con- 

 ditions must be met just as for any other fungous disease. 

 Broadly stated, tliese are (1) the presence of infective material, 

 (2) a host plant in a condition of suscej)tibilit.y, (3) general en- 

 vironmental conditions that are favorable. All rational control 

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

 fungus with reference to these three things. 



Tlie infective nuiterial for Diaporthe parasitica seems to be 

 pre-eminently tlie spores, Avhich are of two types, the pycuospores, 

 sometimes called conidia or summer spores, and the ascospores, 

 or winter spores, ^^'e wisli to know definitely the conditions that 

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

 favorable and under unfavorable conditions, their modes of shed- 

 ding and of transfer, the conditions favorable and unfavorable to 

 their germination, their abilities to establish the fungus upon 

 various materials, and tlie relative importance of the two types 

 in s[>reading the disease. General environmental conditions may 

 liave their effect upon longevity of spores, upon germination of 

 spores, upon rapidity of groAvth of tlie 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 

 individuals, 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 history of the organism 

 may be of interest and im])ortance, aside from any direct rela- 

 tion to tlie setting up of infection. 



