334 



Bulletin 263. 



fungus and future vegetative development is assured. It is only when 

 the vine dies that there is need for reproductive bodies. 



Examination of dead vines, or the dead part of large stems, late in 

 the autumn or early winter will show a great quantity of very small 

 pimples, pycnidia (Fig. 50). These are formed by external growth 

 of the mycelium and are composed of modified mycelial threads. 



Early in the spring, the 

 interior of these bodies 

 (pycnidia becomes filled 

 with hyaline, slightly 

 curved pycnospores which 

 are small and can be seen 

 only with the microscope 

 (Fig. 51). They are vari- 

 able in size and shape and 

 can be seen in Figure 52. 

 They measure from 6.3 to 

 11.2x1.7 to 2.8 micro- 

 millimeters (i mmm = 

 1/25000 inch). In May 

 and June, these spores are 

 mature, and with the ab- 

 sorption of moisture after 

 a rain or heavy dew the 

 gelatinous substance that 

 surrounds them swells and 

 forces the spores out of 

 the top of the pycnidium 

 in a stream. It is easy to 

 find such streams of spores 

 which are one-quarter inch 

 in length or even longer. 



Photo. Oct. 26, 1908 



Fig. 50. — Co'ncord. Pycnidia of the fungus on 

 canes. Loose bark stripped off 



Germination of spores 



The spores when placed in a drop of water will germinate in 18 



hours or less, and the germ tube (Fig. 52) elongates to form a new 



thread of mycelium. If such spores are taken under sterile conditions^ 



*The best success in obtaining pure cultures came by direct transfer method. More 

 than 75 per cent, of transfers made in that way were pure cultures. The 

 poured-plate method was also used and pure cultures obtained in that way. 

 The method was not satisfactory, however, since the spores did not germi- 

 nate in the agar which I had with me in the field and, as they became very 

 hyaline, were difficult to locate. 



