90 MISSOUEI STATE HORTICULTURAL SOCIETY. 



called mycelia. The mycelia of many species is internal; with others 

 it is superficial, or on the exterior of the host or supporting- plant. 



The reproductive bodies are usually the most prominent part of 

 many species of fungi, as they are usually colored and form the redisb- 

 brown powder which causes the host plant to present the rusty ap- 

 pearance. The reproductive bodies firo commonly called spores, but 

 as there are several stages of soine species (especially the rusts) the 

 reproductive bodies of each stage are known under different names, 

 which prevents confusion. 



Thus, there are usually three stages of many of the species be- 

 longing to the order Uredince (rusts, as they are commonly called). The 

 first stage is known as the JEcidium stage. This stage occurs early in 

 spring, and the reproductive bodies are known as (vcidiospores. The 

 second stage occurs in mid-summer and is known as the Uredo stage, 

 and the reproductive bodies of this stage are called uredospores. The 

 third and last stage occurs late in September or October, lives through 

 the winter, germinates the following spring, and gives rise to the first 

 or (ccidium stage. The spores of the last stage are known as the tclen- 

 tospores, which are usually dark colored and from one to many celled. 



Most of the mildews produce two or three kinds of spores, and 

 their growth is quite as remarkable as the growth of the various spe- 

 cies of rust. 



The facts given above will enable you to understand how difficult 

 it is to trace the life history of these parasites, especially as the objects 

 studied are so small that a microscope is necessary to study them. 

 But, despite the many difficulties, progress is slowly being made. A 

 century ago the total number of described species did not exceed GOO, 

 and more tban half of these were included under the old genus Agari- 

 cus, or toadstools. Little or nothing had been done with the more 

 minute species, such as the rusts, mildews, etc. But microscopes were 

 not in use in those days, and without the aid of microscopes little prog- 

 ress could be made. 



Since microscopes have come into more general use, many new 

 species have been described. A few years ago the total number of 

 described species did not exceed 600; the number now has increased 

 to many thousands, and new species are constantly being discovered 

 and classified. 



Prof. Burrell, in a bulletin issued by the Illinois State Laboratory 

 of Natural History, describes about oOO species belonging to the order 

 Uredinw (Rusts), that were collected within the borders of Illinois. A 

 knowledge of the life history of these parasites is of the utmost import- 



