512 SPECIAL PLANT PATHOLOGY 



which measure 10.5 to 13.5^1 by 5 to 6^. The ascigeral stage is less com- 

 mon. The perithecium has a rather dense wall inclosing a number of 

 clavate asci, which are 60 to 8om long (Fig. 183). The ascospores are 

 hyaline, elliptic to sub-rhomboidal in form with granular contents. 

 The fungus has been grown successfully in artificial culture media, but 

 after a few generations, it seems to lose in vitality. 



Preventative measures consist in an occasional renovation of the 

 bag and in the proper regulation of the water supply. Spraying at 

 least six times with Bordeaux mixture (5-5-50) is used with success; 

 especially, if adhesive substances (4 pounds resin fish oil soap) are 

 added to the mixture. 



Grape {Vitis spp.) 



Black-rot (Guignardia Bidwellii (Ell.) V. & R.) .—Wherever the 

 grape is grown this American fungus is a constant menace to the suc- 

 cessful prosecution of the industry. It attacks not only the fruits, but 

 also the leaves, fruit pedicels and stems. The disease, which is most 

 important on the berries (Fig. 184), begins as a small circular brown spot 

 which enlarges until it is 5 to 10 mm. in diameter, when the center of the 

 spot will be found to show a few black pimples which are the openings 

 of the pycnidia, which have now appeared beneath the skin. The 

 spots become darker in color and spread until more than one-half of 

 the fruit surface is involved, when the fruit begins to lose its spheric 

 contour and to shrivel, persistently hanging on the vine sometimes 

 throughout the season. Nearly all of the dark colored grapes are 

 susceptible, such as the universally grown Concord, while some light 

 colored varieties are more resistant. The Scuppernong is apparently 

 entirely resistant. 



As with many of the fungi which attack our cultivated plants, the 

 different stages were known before the. complete life cycles were de- 

 termined and therefore, these stages received scientific names, which 

 are relegated to synonymy, when the life history becomes known 



mature ascospore, showing the usual condition, in which the protoplasm is very 

 coarsely granular. 13, An old ascospore from a dried specimen, having its contents 

 homogeneous. 14, a, A portion of the coarse brown mycelium from the interior of 

 a scalded berry, from which a culture was made December 23, producing pycnidia 

 and ascogenous perithecia of Guignardia vaccinii; b, a portion of younger, lighter 

 colored hyphae from the same berry. {After Shear. C. L., Bull, no, U. S. Bureau of 

 Plant Industry, 1907.) 



