338 Bulletin 263. 



as well as the spores they contain are identical in every respect with 

 those developed normally on the dead stem. 



Behavior of the spores under natural conditions 



We have seen that under artificial conditions spores will grow, pro- 

 duce a mycelial growth and in turn reproduce more spores. Under 

 natural conditions, there are many obstacles that prevent the spores of 

 the fungus from accomplishing their normal function. Were it not 

 so our vineyards would be completely destroyed in a very few years,, 

 owing to the enormous quantity of spores developed on each diseased 

 stem, and the very wide geographical distribution of the disease. 



The gelatinous substance that aided in getting the spores outside the 

 pycnidium now becomes a hindrance. When exposed to air the sub- 

 stance dries and holds the spores in a firm mass, thus preventing 

 ready dissemination by means of the wind. Water seems to be neces- 

 sary to free the spores and this only comes with a rain or heavy dew. 

 Moreover, the moisture which allows dissemination is also necessary for 

 germination. So far as is known, one of three fates awaits the spores 

 which are thus developed and extruded : 



(i). Some are washed by rain to green parts of the vine where, if 

 conditions remain favorable, infections are produced (Fig. 48). The 

 lesion begins as a small discolored spot which soon becomes brown or 

 even black, and either forms a depression or a longitudinal v-shaped slit. 

 There may be tinges of red about the margin of the lesion, but there 

 is never a bright red elevated margin as in the case of the anthracnose 

 on stems, 



(2). Others are washed to a wound or dead stub of the vine and 

 there may grow and develop mycelium. No positive proof of this fact 

 is yet at hand. Infection experiments are now under way to determine 

 this point, if possible. The fungus progresses so slowly that it may be 

 a number of years before results are obtained. 



(3.) By far the greater part of the spores are washed free by the 

 rain and lodge in places where growth is not possible and die. 



Other means of dissemination and infection 



Observations in the field lead the writer to believe that spores do not 

 play the most important part in the dissemination of the disease in the 

 vineyard. One can frequently find cares when the disease seems to 

 be localized in an arm (Fig. 49), or in the two lower arms (Kniflfen 

 system), while all other parts seem to be healthy. Since the trimmer 



