MARKET DISEASES OF VEGETABLES. 9 



Fungi bear their spores in various ways. In the simpler 

 types the spores are borne on the surface of the attacked 

 plant as a powdery or dusty covering such as one sees in 

 blue mold (Penicillium) and gray mold (Botrytis). Some, 

 such as Rhizopus nigricans, bear their spores in special cases 

 called sporangia, (singular, sporangium). The summer 

 spores of many fungi are known as conidia (singular, 

 conidium). 



In other fungi, spores are produced in slimy heaps on 

 little pads or cushionlike bodies known as acervuli (singu- 

 lar, acervulus) . These are especially marked in the anthrac- 

 noses. Still other fungi bear their spores in special flask- 

 shaped bodies on or at the surface of the diseased portion 

 of the attacked plant. These appear as dots, or pimple-like 

 bodies and are known as pycnidia (singular, pycnidium). 

 They are conspicuous in the late blight spots on celery, the 

 fruit rot of egg plant, the Phoma rot of tomatoes, and the 

 black rot of apples. The special spore-bearing structures 

 of fungi are known as fruiting bodies. The fruiting bodies 

 which result from fertilization and contain the winter spores 

 do not occur generally under market and storage conditions. 



There are four classes of fungi, Phycomycetes, Ascomy- 

 cetes, Fungi Imperfecti, and Basidiomycetes. Most of the 

 fungi with which we will deal belong to the third of these 

 groups. 



The Life Processes of Bacteria and Fungi. 



The protoplasm of bacteria and fungi lacks chlorophyll 

 and therefore cannot manufacture its own food, but must 

 obtain it from green plants, either directly or indirectly. It 

 obtains its food and energy by digestive and respiratory 

 processes from the tissue attacked. This digestive and 

 respiratory action of bacteria and fungi is popularly known 

 as fermentation. Bacterial rots generally are accompanied 

 by putrefactive odors due to the breaking down of protein 

 compounds. 



The attack upon living tissues by parasites leads to a dis- 

 turbance in the functions, structure, and composition of the 

 attacked plant, in other words, to disease. The diseased 

 areas produced by parasites or other causes are known as 

 lesions. At present only those produced by the action of 

 parasites will be considered. A lesion may be a leaf or 

 pod-spot, a wart, a soft or dry-rot, or a canker, depending 

 upon the parasite, the external conditions, and the nature 

 and response of the affected host tissues. Soft rot of the 

 carrot, for example, consists of lesions caused by Bacillus 

 carotovorus. These bacteria secrete ferments or enzymes 

 which digest or dissolve the cementing substances between 

 the carrot cells and disintegrate the tissue into a soft, slimy 

 mass. 



In other diseases the lesions arise in a different manner. 

 In anthracnose of the cucumber, for example, the hyphae 



