CONSTITUENTS AND HABITS 



17 



(notably Colly bia vehttipes) will develop in weather that is only a 

 little above the freezing point, it commonly requires warm wet 

 weather to facilitate the growth of an abundant crop of fungi, and 

 in temperate climates the months from July to October are most 

 prolific in the growth of the higher fleshy forms. On the other 

 hand, many of the black fungi (Sphaeriales) develop their asco- 

 spores during the winter, the period from February to May being 

 particularly favorable for their collection. 



Fungi inhabit nearly every form of matter living or dead. De- 

 caying wood and other vegetable matter, dead flies and fish, sac- 

 charine fluids like preserved fruits, greasy bones, food stuffs like 

 bread and cheese, all furnish the medium in which saprophytic 

 species develop and thrive. Parasitic forms live on flies, grass- 

 hoppers, fish, birds and even man among the animals ; others 

 attack pollen grain, diatoms, pond scums and other algae, and 

 even other fungi, and every spermaphyte from the conifers to the 

 composites has one or more parasitic species living at its expense. 

 We have rusts, mildews, moulds, smuts and leaf spots not only 

 on every known cultivated plant, but on the wild plants of moor, 

 of forest and of bog, their name is legion. We can distinguish three 

 ordinary types of parasitism : 



1. That of internal free parasites floating or swimming in the 

 cell sap of plants or the juices of animals. To this group belong 

 many of the bacteria. Allied to these in habit are the unicellular 

 myxos and Synchytria which often live inside the walls of a single 

 cell of their host. 



2. That of internal fixed parasites forming mycelium within the 

 tissues of other plants and appearing at the surface only for pur- 

 poses of reproduction. Such are the rusts and smuts of grain 

 and most of the common injurious fungous diseases of cultivated 

 plants. Their presence is shown by discoloration (yellowing or 

 browning) of the tissues of the plant attacked, and often by thick- 

 ening or other deformation of the tissues, sometimes, even by the 

 formation of galls. In some cases, as in many of the rusts, the 

 affected area is slight and confined to the immediate region about 

 the point where spores are ultimately formed. In other cases, as 

 in some of the smuts, the mycelium of the parasite is more ex- 

 tended throughout the tissues of the plant and the parasite does not 

 disclose its presence in the host until the time when spores are pro- 



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