208 



Bulletin 



253- 



hidwellii) produces its winter or resting stage on the black hard mummied 



grape berry or its pedicel (Fig. 177). Its spores are contained in tubular 



sacs, each sac or ascus containing 8 spores. A large number of the sacs 



(20-50) are grouped close together and surrounded by several layers of 



thick-walled cells. Protection is thus 



assured for the spores or germs. 



This cluster of sacs with their thick 



protection appears to the naked eye 



as a very small pimple on the surface 



of the mummied berry. Every berry 



may have a hundred or more such 



pimples, which are technically known 



as perithecia. (See Fig. 178.) 



Some of the spores are ripe and 



ready to grow about the time the 



first three or four leaves on the new 



shoots appear. Others do not ripen 



until later. If the first fail to start 



the disease, those produced later will. 



This succession of maturity of 



spores is such that as late as October 



winter-spores just in condition to grow 



can be found. This at least was true 



during the past season, which was very 



dry. The fungus, just as any field 



Fig. 177 — The mummy berries, on crop, must have moisture in order to 

 which the fungus passes the winter. p-rnw 



The accompanying illustration (Fig. 178) is of a thin section through 

 the middle of the perithecium, taken at a stage when only a few of the 

 sacs have mature spores. In the others, the spores are not yet formed. 

 The section is greatly magnified and shows the condition when water is 

 added. In the vineyard, this would mean whenever rain or dew lodged 

 on the mummied berry. The sacs that contain ripe spores become gela- 

 tinous and, being swelled by the addition of water, protrude themselves 

 beyond the wall of the perithecium. For this reason, poisonous sub- 

 stances sprayed on the mummies are not effective, since they do not 

 touch the germs. 



Distribution of the germs. 



Now a most interesting thing, as seen under the microscope, takes 

 place. The spores are crowded to the upper end of the ascus and the 

 one at the tip can be seen to be moving. It is as though the spore 



