234 



PRACTICAL BOTANY 



masses are poisonous, and, as ergotine, are sometimes us.ed for 



medicinal purposes. A parasite known as root rot (Thielawa ba- 

 sicola) attacks the roots of tobacco, horse- 

 radish, and violets, and of peas and other 

 leguminous plants. 1 The rose and peach 

 mildew (^SphcerotJieca pannosa)? which oc- 

 casionally appears as light-colored downy 

 patches upon the fruit of the peach, attacks 

 the leaves of roses and is very destructive. 

 The wilt disease of cotton, cowpea, and 

 watermelon (Neocosmospora vasinfecta) 3 is 

 widely distributed over the Southern states 

 and attacks the vascular bundles in such a 

 way as to cut off the plant's water supply. 

 A common disease of plum and cherry 

 trees is black knot (Plowriglitia morbosa). 4 

 The familiar and very destructive dark 

 and shrunken patches on the fruit of the 

 apple are due to bitter rot (Grlomerella 

 rufomaculans)? The value of fruit des- 

 troyed by it sometimes amounts to millions 

 of dollars in a single year. 



In addition to the conidial forms already 

 considered in connection with their asco- 

 sporic forms and used as types of their re- 

 spective groups, there remain thousands of 

 species whose life histories are not known. 



Many are saprophytes and many are parasites, some of which 



are very destructive to crops. 



1 Clinton, G. P., "Root Rot of Tobacco," Conn. Agr. Exp. Sta., 1906. 



2 "Peach Mildew," Bulletin 107, Colo. Agr. Exp. Sta., 1906. 



8 " Wilt Disease of Cotton, Watermelon, and Cowpea," Bulletin 17, Divi- 

 sion of Vegetable Pathology, U. S. Dept. Agr., 1899. 



*Lodeman, E. G., "Black Knot," Bulletin 81, Cornell University Agr. 

 Exp. Sta., 1894. 



6 "The Bitter Rot of Apples," Bulletin 44, Bureau of Plant Industry, 

 U. S. Dept. Agr., 1903. 



FIG. 189. Ergot which 



has grown on a head 



of rye 



After Duggar 



