DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 509 



while the other spore forms are represented by urediniospores and 

 teliospores. All parts of the green cotton plant may be rusted, 

 spreading to the new leaves as they are formed. Small rounded, or 

 angular, purplish-brown spots appear on the upper leaf surface and the 

 urediniospores are borne in pustules just beneath the epidermis on the 

 under leaf surface, which finally ruptures and sets them free. The 

 varieties of cotton grown in the Southern United States are partially 

 immune, while the tropic varieties are more susceptible. It is rec- 

 ommended that the cotton grower destroys all rubbish in his fields 

 and adopts a system of field culture in which only vigorous plants will 

 be obtained. 



Cranberry {Vacdnium macrocarpon, Ait.) 



Gall {Synchytrium vaccina, Thomas) (Fig. 230). — The fungus which 

 causes cranberry gall is a very much reduced phycomycetous one, which 

 attacks the young stems and leaves, as well as flowers and fruit of the 

 cranberry. It also lives on other ericaceous plants. The galls are 

 small in size, reddish in color and are produced in great numbers on the 

 parts affected. The fungous body is much reduced, consisting of a 

 single cell which becomes a zoosporangium. The presence of this 

 parasitic cell in the tissues of the host is to produce a small gall. Later 

 the zoosporangium develops a mass of swarm spores, or zoospores, 

 which escape into the water. Infection, therefore, probably takes 

 place when water is abundant. 



Scald {Guignardia vaccinii Shear). ^ — The scald fungus (Figs. 182 

 and 183) may attack the very young fruit and even the flowers of the 

 cranberry and annually does considerable damage to the growing crop, 

 as the annual loss has been estimated at $200,000. The pycnidia 

 are usually found upon such parts. The berries are characterized by 

 watery spots, which may remain small under certain conditions, while 

 under others it spreads quickly, often concentrically until the whole 

 berry becomes soft. The leaves are also spotted with irregular brown 

 spots within which the pycnidia are found. 



The pycnidial stage is a characteristic Phoma, or Phyllosticta, 



measuring 100 to 120^ in diameter. These are scattered over the 



affected surface and abundant hyaline, obovoid pycnospores are formed, 



• Shear, C. L. : Cranberry Diseases. U. S. Bureau of Plant Industry. Bull. 



no: 1-64, 1907. 



