2 MISC. PUBLICATION 1, U. S. DEPT. OF AGBICULTUEE 



THE LIFE STORY OF A RUST 



In the spring, when plants be^in to grow, there is a little visitor 

 that comes and makes itself at home on a barberry leaf. This tiny 

 visitor is a rust sj^ore of the first stage of stem rust. This sporr, 

 like many more of its kind, has just been produced by the black 

 spores of the rust which have rested through the Avinter on stubble 

 and old straw. (Fig. 1.) 



This tiny spore rests on the leaf and takes a bath in a raindrop 

 or in dew. When it has soaked for a few hours it sprouts, and a 

 little rootlike tube called a Jiypha j^ushes out of it and reaches into 

 the barberry leaf. It sucks food out of the inside of the leaf, tuul 

 grows into a rust plant. In order to be heahhy tlie barberry leaf 

 needs this food for itself. So, while the rust plant is growing 

 strong, the barberry leaf becomes weak and sick. 



Such a starved, sick barberry leaf soon has a yellowish spot on 

 top and some little yellowish cup-shaped growths on the imderside. 

 This is the second stage of the rust. These growths lie close to- 

 gether in clusters and are called cluster cups. (Fig. 2.) They are 

 tilled with yellow spores that grow in rows like beads in a chain. 

 When they are ripe these spores are shot out into the air like smoke 

 from a gun, and the wind lifts and carries them as it does smoke. 



The spores that are shot out of the cluster cups can not grow on 

 a barberry leaf. This seems very strange, as the barberry leaf has 

 tlie right sort of food for the cluster cups themselves. 



The habit of these yellow spores that come out of the cluster cups 

 is to live on plants that belong to the grass family, and not on any 

 other kind. Such of the spores as are blown to barberry bushes or 

 oak trees or potatoes or anything in the world except some kind of 

 grass can not grow into rust plants, but die while they are spores. 

 But there are thousands and thousands of spores that, in tiny clouds, 

 come puffing out of the cluster cu}is, and many of them are brought 

 to wild or cultivated grasses. If there are any wheat plants grow- 

 ing in the neighborhood of a barberry bush, th<'v are sure to be dusted 

 wit!) spores that are blown over from the cluster cups. 



A\'hen one of these spores comes to rest on a wheat stem or leaf, 

 and soaks for four or five hours in a drop of rain or dew, it starts 

 to grow. It sends out a little tube or hypha that grows along the 

 outside of the stem until it comes to a breathing pore. Then it 

 glows into the pore, and helps itself to the food in the inside of the 

 wheat plant. Of course the wheat plant needs this food, and, if 

 there are many rust plants growing on it and stealing its food, it 

 becomes weak and sick. After a spore starts its hypha into the 

 wheat it takes about a week or 10 days for the fungus to grow into 

 a rust plant old enough to produce more ripe spores. These spores 

 grow in little spots called fnii<tules. 



A sick wheat plant soon looks as if it had little blisterlike pustules 

 all over its bo«ly — on its stems and leaves. In a few days these 

 pustules open. They are filled with rij)e spores which are rusty 

 red in color. (Fig. 3.) This is the third stage of stem rust and is 

 known as the red stage. 



These red sj)ores blow to other wheat plants, and the same thing 

 happens. So, about once every 10 days, there is a fresh crop of red 



