184 



STUDIES IN CRYPTOGAMS 



325. 



Sori containing teleu- 

 tospores of wheat 

 rust. 



true parasite, affecting wheat and a few other grasses. The mycelium 

 here cannot be seen by the unaided eye, for it consists of threads 

 which are present within the host plant, mostly in the intercellular 

 spaces. These threads also send short 

 branches, or haustoria (180), into the 

 neighboring 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. 

 325), from the ends of numerous crowded 

 mycelial strands just beneath the epider- 

 mis 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. 

 326). Since they are the resting- or win- 

 ter-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 sev- 

 eral times the length of the spore and terminates in a blunt 

 extremity (Fig. 327). This germ-tube, or lasidium, 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. 327 a 

 germinating spore is drawn to show the basidium, &, divided 

 into four cells, each producing a short branch 

 with a little spore, 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 fol- 

 lows that if no barberry bushes are in the 

 neighborhood the teleutospores finally perish. 

 Those which happen to lodge on a barberry 

 bush germinate immediately, producing 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 



326. 



Teleutospore 

 of wheat rust. 



327. Germi- 

 nating te- 

 leutospore 

 of wheat 

 rust. 



