CH. VII, 5] NATURE OF PLANT DISEASES 367 



Among genuine monstrosities, twin fruits, which are rather 

 common, result from a partial fission of one (Fig. 146 and 

 page 198). A genuine fasciation, producing several distinct 

 lobes, occurs, in highly cultivated Strawberries, and also 

 in Pineapples, as earlier pictured (page 198). Two-storied 

 fruits also occur as result of proliferation (page 202), though 

 sometimes a leafy branch occurs in place of the second fruit ; 

 and the Navel Orange is an imperfect case. Apples and 

 Cucumbers occasionally produce bracts on their sides (page 

 202). Sometimes the carpels do not all unite in the pistil, 

 but some remain separate, as is said to occur rather often in 

 Oranges. Ears of Corn sometimes have tassels of male 

 blossoms on their upper ends, and sometimes branch at the 

 base. And other monstrosities less common are met with 

 of which some can be propagated. 



5. THE NATURE AND CURE OF PLANT DISEASES 



Plants are subject to many diseases, which appear perhaps 

 in fruits more prominently than elsewhere. 



Plant diseases, which are studied very thoroughly in agri- 

 cultural institutions under the name of PHYTOPATHOLOGY, 

 or simply PATHOLOGY (page 4), fall into three general cate- 

 gories, those caused by parasitic Fungi, those of purely 

 physiological origin, and those of which the nature is still 

 unknown. 



Parasitic Fungi, including Bacteria, cause the great ma- 

 jority of the worst plant diseases, notably Rusts, Blights, 

 Smuts, Mildews, Wilts, Rots, Cankers, Crown Galls, Black 

 Knots, Scabs, Spot and Blotch diseases, and other special 

 diseased growths, the description of which will be found in 

 Part II of this book. The very small spores by which these 

 Fungi reproduce are carried everywhere by winds, and when 

 thus brought to a suitable host plant they germinate, and 

 the haustorial threads enter the plant body either through 

 the stomata, the water pores, or some injury of the surface, 

 or even at times, though rarely, directly through the epi- 



