224 GRASSES OF IOWA. 



We add here also Brefeld's* conclusion. His experiments 

 are divided into four series from which the following conclusions 

 were drawn. First. — Very young seedlings could be infected to a 

 slight extent; older ones not at all. Second. — Successful infec- 

 tion in rolled up young leaves, when plants were a foot high. 

 Third. — Successful in young inflorescence. Fourth. — When 

 brace roots were in right condition they took the disease. 



"According to this, the final result of all the infections with 

 corn smut on maize is entirely different from the previously 

 described results with smut fungi living exclusively in the 

 grains. The smut germs come to full development and pro- 

 duce smut pustules and spore beds on every spot of the still 

 undeveloped parts of the plant into which they have pene- 

 trated. The action of the germ is narrowly localized — only 

 those parts of the young plant become smutty which have been 

 attacked directly by the fungus germs; all the rest remain 

 normal and sound. The formation of the smut pustules begins 

 quickly, at longest three weeks after the infection." 



"The complete result of all the here-cited infection experi- 

 ments with dusty smut, millet, and corn smut affords, in the 

 first place, indisputable proof that the germs of smut fungi 

 which live saprophytically outside of the host plants can pro- 

 duce smut diseases." 



"When the smut was nourished saprophytically longer than 

 a year in continual reproduction outside of the host plant, then 

 only did the outgrowth of the conidia into germ tubes cease. 

 Along with this the power of infection was extinguished, i. e. , 

 with the disappearance of a comprehensible morphological 

 character, for the germs can only penetrate into the host plants 

 by means of their germ tubes. " 



"The earlier view that only the young seedlings of the host 

 plants are receptive to the fungus germ has not been sus- 

 tained. On the contrary, the fungous germs can penetrate 

 into all sufficiently young parts of the host plant." 



Mycelium. — The fungus vegetates in the interior of the plant 

 by what is termed the mycelium; a single thread being known 

 as a hypha. In its early stages these fine threads penetrate 

 chiefly batween the cells of its host, sending short branches 

 into the cells; these are known as haustoria. These are fre- 

 quently branched, and may extend as far as the nucleus and 



♦Untersuchungen aus dem Gesammtgeblete der Mykologle. Heft XI. Smith. .Tour, 

 of Myc. No. 4. 6: 162. 1890. 



