308 USTILAGINEAE. 



out, and the grains are somewhat compressed. In earlier 

 stages of development the diseased ears are less easily dis- 

 tinguished, but they grow more rapidly than the normal, their 

 ovaries are earlier formed, and have a dark greenish-brown 

 colour. According to Kiihn,^ the ears in their earlier stages, 

 as they emerge from the leaf-sheath, possess abnormally thickened 

 seed-coats, especially towards the apex, while in section they show 

 a dark-green colour. He also found the grains to be replaced by 

 a white and easily detachable mass of fine mycelium. Spores 

 are formed as swellings on the ends of the sporogenous hyphae, 

 and into these the plasma-contents of the hyphae pass over. The 

 mature spores are dark-grey and spherical, with netted markings 

 on the episporium. They germinate in water, and produce a 

 promycelium of varying length. The conidia arise as a whorl 

 of thread-like branches on the end of the promycelium, and into 

 them all the protoplasm passes over, while the promycelium, 

 after being cut off by a cross septum, disappears, leaving the 

 conidia as isolated bodies (Fig. 167). The conidia become united 

 in pairs, frequently before isolation. After fusion comes germina- 

 tion, and the emission of a filament from the end of which 

 sickle-shaped conidia are abjointed. Kiihn states that these 

 conidia, as well as the whorled primary conidia, if placed in a 

 damp atmosphere, can give rise to a hypha capable of infection. 

 In water, however, the hyphae continue to grow longer, the 

 plasma from the older parts passing over to the younger, and 

 no conidia are formed (Fig. 167). 



The conidia which remain unpaired were found by Brefeld to 

 behave similarly to those which pair, except that the resulting 

 germ-tubes and conidia remained smaller. Spores refuse to 

 germinate in nutritive solutions. Conidia grown in water 

 cultures and placed afterwards in nutritive solutions, give off 

 a fine mycelium, from which short, lateral, aerial branches 

 become cut off by septa, and devote their contents to the pro- 

 duction of a few sickle- shaped conidia ; these are easily detached, 

 and produce a mycelium capable of giving off further conidia 

 in a manner similar to that just described. 



The investigations of Brefeld have also given the interesting 

 result that hyphae which produce conidia may also give rise 

 to spore-like bodies. The hyphae, after growth in length has 



' KUhn, Die Krankheitm d. Kidlurgeu'achse , 185S. 



