92 



in the autumn are allowed to remain exposed to the 

 weather throug-h the winter, they will, under suitable con- 

 ditions, germinate in a few hours in March or April. In 

 this case the process of germination of the spore differs 

 from any of those dealt with in previous chapters. Each 

 of the two cells of the spore sends out a delicate tube, 

 which, after growing to two or three times the length of 

 the spore, becomes divided into four cells or segments. 

 Then a delicate peg-like branch is put out from each of 

 these segments, and a minute, oval spore is formed at the 

 tip of each peg. The question now arises as to what 

 becomes of these teleutospores and the small oval spores 

 or sporidia they produce. For many years this v/as not 

 understood, although trials again and again proved that 

 the teleutospores or their sporidia were unable to cause 

 new infection on the wheat plant. 



The clue to the problem was discovered by De Bary 

 m the old belief of farmers that outbreaks of rust were 

 m some way connected with the presence of barberry. He 

 first made a careful study of the yellow fungus which 

 occurs on barberry, and then proved the connection of this 

 with the rust on wheat. If one of the diseased areas on 

 the barberry is closely examined it is found to arise on 

 a swollen part of the leaf, and on the under side a number 

 of small, yellow, cup-like bodies are produced. From 

 these cluster-cups yellow spores, known as aecidiospores, 

 are liberated as a fine dust. A section through the diseased 

 area shows that the cluster-cups arise as round masses of 

 fungal filaments beneath the skin of the leaf. Within 

 the ball of fungus, aecidiospores are produced in chains^ 

 and when this growing ball bursts the skin of the leaf, it 

 opens at the apex and the edges turning back g^ive the 

 structure the appearance of a minute cup or bowl. The 

 aecidiospores arise from threads at the base of this, and 

 as they ripen and are set free new spores are produced. 

 Now^ De Bary discovered that when sporidia from the 

 teleutospores on wheat are sown on barberry leaves in the 

 spring, infection takes place and the cluster-cups just 

 described are produced in two or three weeks. Not only 

 did he prove this, but he also showed that when the 

 aecidiospores from the cluster-cups are sown on the leaves 

 of wheat, they germinate, and like the uredospores send 

 g;;erm tubes through the stomata and thus infect the leaf. 

 Pustules containing uredospores and later teleutospores 



