226 MANUAL OF POISONOUS PLANTS 



tube enters by way of the stomata, or the so-called breathing pores. The germ 

 tubes produced by the spore of Aecidium berberidis are simple or branched, and 

 in fourteen days usually give rise to the uredo spores, which occur in definite 

 spots called sori. These spots occur in great numbers along the veins of the 

 leaves. Before breaking open, the tissues of the leaf are somewhat paler at 

 those places. The nourishment afforded by the host causes a vigorous mycel- 

 ium to form, which soon collects in places, pushes the epidermis out, and an 

 orange-colored pustule is formed which is known as the uredosorus. 



A section through a diseased sorus shows that an abundance of the vegeta- 

 tive mycelium grows between the cells of the plant, and in some cases haustoria 

 penetrate them. This pustule contains a large number of 1-celled, round or 

 elliptical, spiny, orange colored spores, the uredospores. The spores have two 

 membranes, the outer exospore being provided with wart-like projections, while 

 the inner endospore is provided with several pores through which the germ 

 tube appears. These spores germinate in from three to four hours and can 

 thus start a general infection. These spores, carried by the wind, rain or in- 

 sects to another part of the same or another plant, germinate, the germ tubes 

 branch and spread over the surface, but the tube cannot enter the host — a 

 grass of some kind, such as wheat, oats or barley — unless it reaches the opening 

 of the stoma, since it cannot bore through the epidermal cells. A single sorus 

 contains hundreds of spores, and as a single plant may contain hundreds of 

 pustules, it can readily be seen that rust must become quite general. 



The red rust stage is followed by the black rust stage, known as the 

 teleuto stage. The sori are brownish-black in color, and frequently occupy 

 the same place that the uredo stage did. The spores are dark brown in color, 

 two-celled and smooth, having attached to them a persistent stalk known as 

 the pedicel. The teleutospores do not germinate till the following spring, when 

 each cell produces a germ tube, the promycelium bearing lateral spores, sporidia. 

 These sporidia, when in contact with the barberry leaf, enter by boring their 

 way through the epidermal cells. 



The barberry cluster cup fungus, and its connection zvith common grass 

 rust. It is not absolutely necessary for the common grass rust to have its first 

 stage on the barberry, yet experiment has shown beyond doubt that it does 

 occur on that plant. The theory has been advanced that appearing in one of 

 its stages on the barberry gives the parasite new vigor. It is not improbable 

 that in some places the mycelium or vegetative part of the fungus may be 

 perennial in the tissues of grasses, as it is with many other fungi, probably 

 this is true in southern looalities. Beyond question this rust produces spores 

 during the entire year in our southern states, and on the approach of early 

 spring gradually moves northward. It may also be mentioned that in the west 

 this rust certainly does not appear before the cluster cup fungus on the barberry 

 appears. It is usually eight or ten days later, and then appears to a limited ex- 

 tent only. Rust often appears where barberry does not occur within hundreds of 

 miles. This was especially noticeable during the early history of grain culture 

 in the northwest. Rust follows a general infection. 



Distribution and hosts. This fungus has been found not only upon wheat 

 but also upon several species of Bromus, Trisctutn and Triticnin spelta. Its 

 distribution cannot be given because in most cases the P. riibigo-vcra included 

 this as well as the P. glumarum. It has been intimated above that the uredo- 

 spores make their appearance on young germinating plants in the fall, but it 



