FUNGI 



191 



352., 



Son containing teleu- 

 tospores of wheat 

 rust. 



within the host -plant, mostly in the intercellular spaces. These 

 threads also send short branches, or haustoria (194), into the neighbor- 

 ing cells to absorb nutriment. 



The resting-spores of wheat rust are 

 produced in late summer, when they may 

 be found in black lines breaking through the 

 epidermis of the wheat-stalk. They are 

 formed in masses, called sori (Fig. 352), 

 from the ends of numerous crowded mycelial 

 strands just beneath the epidermis of the 

 host. The individual spores are very small 

 and can be well studied only with high 

 powers of the microscope (x about 400). 

 They are brown two-celled bodies with a 

 thick wall. (Fig. 353.) Since they are the 

 resting- or winter-spores, they are termed 

 teleutospores ("completed spores"). They 

 usually do not fall, but remain in the sori 

 during winter. The following spring each 

 cell of the teleutospore puts forth a rather stout thread, which does 

 not grow more than several times the length of the spore and termi- 

 nates in a blunt extremity. (Fig. 354.) This germ-tube, promycelium, 

 now becomes divided into four cells by cross-walls, which are formed 

 from the top downwards. Each cell gives rise to a short, 

 pointed branch which, in the course of a few hours, forms a 

 single small spore at its summit. In Fig. 354 a germinating 

 spore is drawn to show the basidium, b, divided into four 

 cells, each producing a short branch with a little sporidium, s. 

 A most remarkable circumstance in the life-history of 

 the wheat rust is the fact that the mycelium produced by 

 the teleutospore can live only in barberry 

 leaves, and it follows that if no barberry 

 bushes are in the neighborhood the sporidia 

 finally perish. Those which happen to lodge on 

 a barberry bush germinate immediately, pro- 

 ducing a mycelium which enters the barberry 

 leaf and grows within its tissues. Very soon 

 the fungus produces a new kind of spores on 

 the barberry leaves. These are called aecidio- 

 spores. They are formed in long chains in little fringed cups, or xcidia, 

 which appear in groups on the lower side of the leaf. (Fig. 355.) These 

 orange or yellow aecidia are termed cluster-cups. In Fig. 356 is shown 



354. Germi- 

 nating te- 

 353. leutospore 



Teuleutospore of wheat 

 of wheat rust. rust. 



