UREDINALES 87 



two cells instead of one, and (3) In having thick walls. {PI. 6. f. d.) 

 These spores are known as the teleutospores and their function is 

 normally that of a resting spore which will carry the life of the fun- 

 gus over an unfavorable period, namely, the winter season. This 

 black rust remains on the straw or stubble until the early warm 

 days of the following spring, when the teleutospores germinate, 

 developing a short promycehum on which as on basidia the fourth 

 form of spores is produced. (/Y. 6. f. p.) These so-called 

 sporids are carried by the wind and if any of them chance to fall 

 on the young leaves of the barberry just unfolding, they germinate, 

 and their mycelium enters a stoma and becomes a parasite in the 

 barberry which will in like manner develop cluster-cups as before. 

 Thus in an endless cycle does the wheat rust carry on its round 

 of miserable dependent existence. Other aecidial forms have a 

 similar relation to species of the genus Uromyces which differs from 

 Puccinia in having one-celled teleutospores. (/*/. 6. f. 10.) 



Another case is seen in the orchard-rust. In summer many 

 apple trees show bright yellow spots often a quarter of an inch 

 wide on the surface of the leaves. This so-called rust is often so 

 abundant that the foliage of the apple-tree has a distinct yellow 

 tint in midsummer. A little later in the season these yellow spots 

 produce a series of tubes very like the shorter ones of the cluster- 

 cups except that they open by a series of chinks or fissures. 

 Their spores scattered by the wind will germinate on the red 

 cedar {Jiniiperus) and produce gall-like swellings, popularly 

 known as cedar-apples which show themselves in early spring and 

 later become covered with yellowish brown projecting masses of 

 spores. As the later spring rains come on, these spore-masses 

 swell into long gelatinous bodies in which the spores they con- 

 tain germinate and produce the secondary spores in a manner 

 quite analogous to the teleutospores of the wheat-rust. These 

 sporids become free and may be carried back by the wind to the 

 apple and there produce anew the centers of infection of the apple- 

 rust. The more common cedar-apple, Gymnosporangiiini ina- 

 cropus, is an annual gall so that there is a necessity for a double 

 transfer of the spores from host to host each season. In G^ glo- 

 bosicni the gall is perennial and successive crops of teleutospores are 

 produced year after year in the same gall. 



Not all rusts show this heteroecism, but produce their succes- 



