MARKET DISEASES OF VEGETABLES. 61 



mind that potatoes consist of living cells and should not be 

 handled like stones. 



POTATO: ENLARGED LENTICELS. 



Cause : Excessive water supply during the growing season. 



This is marked by flat, pimple-like swellings, which occur 

 at the lenticels of tubers. These swellings are formed by 

 proliferation of cells lining the cavity of lenticels. Normally 

 these cells remain dormant but they may enlarge and divide 

 if potatoes are grown in very wet soil or if the soil becomes 

 waterlogged after the tubers are formed. If this process 

 continues long enough a mass of cells protruding above the 

 tuber surface is formed. 



At first these cells are quite soft, whitish in color, and 

 quite easily rubbed off. Later they harden and become 

 brown and corky. 



Potatoes showing enlarged lenticels are objectionable 

 because of bad appearance of the stock. Their food value 

 is not impaired, since the swellings are superficial. 



POTATO: FLEA-BEETLE DISEASE. 



Cause: The larva of the flea beetle (Epitrix cucumeris 

 Harr.). 



In the simplest cases flea-beetle injury is marked by corky 

 pimples or raised places on the tuber. At times the surface 

 of such pimples is slightly broken. In the more Complex 

 and advanced stages the surface of the tuber is a mass of 

 pimples and of channels or furrows formed by breaking of 

 the skin. The margins of such furrows and channels fre- 

 quently are elevated and swollen so that the whole furrow 

 stands above the surface of the tuber. This type of injury 

 frequently is known as worm tracks. 



By cutting into the pimples or furrows brown, tough 

 splinters of corky tissue are found extending perpendicu- 

 larly into the tuber tissue. Sometimes these splinters are a 

 fourth of an inch in length. Their presence serves to differ- 

 entiate the simple, pimple stage of flea-beetle injury from 

 slight nematode injury, and the furrowed type from other 

 tuber diseases such as scab, grub injury, or wire-worm 

 injury. 



Flea-beetle injury is most frequent in Colorado potatoes. 

 It injures the appearance of potatoes and generally -necessi- 

 tates very deep paring. 



POTATO: NEMATODE DISEASE. 



(See Nematode Disease). 



RADISH: BLACK ROOT. 



Cause: A fungus (Rheosporangium aphanidermatum). 



This disease of radish roots is characterized by blackened 

 regions of varying size which may be rather superficial, or 

 may extend deeply into the root. The darkened tissue is 



