Communications. 291 



few days a short stem, bearing a crop of other spores of very 

 much smaller size. To avoid confusion we will call these by 

 their scientific name — sporidia, while the parent spores are 

 styled tehutospores. The sporidia have never been known 

 to grow upon the grass or grain ; but when they find their 

 way to the leaves of a barberry bush they soon begin to 

 germinate, the filaments enter the tissue of the leaves, and in the 

 course of a few days make themselves manifest on the under sur- 

 face of the leaves, in what are known as " cluster cups." The inte- 

 rior of these pretty little cups is closely packed with spores of a still 

 different kind, which are called the acidium spores. These in 

 turn will not grow upon the barberry, but when they fall upon a 

 blade or stalk of grain, they soon germinate and produce the yel- 

 low rusty covering so often seen, caused by a multitude of another 

 form of spores, called uredo spores, clustered upon the surface. 

 In this, the true rust state, the fungus first consists of minute fila- 

 ments, which run in all directions through the tissue of the grain 

 plant, stealing its nourishment as they go, and is noticeable to the 

 naked eye only when these threads break through the epidermis 

 and bear the yellow or orange uredo spores. The rapid and de- 

 structive development of this fungus depends much upon the 

 weather. Should there be a series of warm showers, or a muggy 

 atmosphere, just at the time the grain plant begins to form its 

 grain, the growth of the rust plant is especially favored. It ab- 

 sorbs rapidly the food which is on its way to the seeds, and uses 

 it up in producing a vast number of spores upon the surface of 

 the leaves and stalks, at the expense of an empty head of husks 

 at the top. Later in the season, from the uredo state the final 

 perfect teleutospores are produced, thus completing the circuit of 

 life in this little rust plant. Long before rust was discovered to 

 be a plant, farmers had noticed that there was a close relation be- 

 tween it and the barberry ; and at present the latter is being 

 rapidly destroyed, with good results, though it can scarcely be 

 expected that the rust plant will thereby become extinct, as prob- 

 ably the tecidium state grows on other plants than the barberry, 

 though not as yet discovered elsewhere. 



The plant is an excellent illustration of polymorphism, so com- 



