Head S?)!!it of Maize. 



CHAPTER XVIII. 



Head Smut of Maize. 

 {Sorosporium reilianum (Kuehn) McAlp.) 



This is the only known smut of maize known at present in Australia, and 

 it is spreading in districts where maize is largely grown. It attacks the cobs 

 and tassels (Plates XII., XIII.), and is usually confined to them, but, in ex- 

 ceptional cases, a few patches of smut may appear on the upper leaves. The 

 smut is enclosed at first in a pinkish membrane, which soon ruptures in order 

 to allow the escape of the spores. It is distinguished from American Corn 

 smut [Ustilago zeae (Beckm.) Unger.) by not enlarging the ears and forming 

 large smut boils, by generally confining itself to the inflorescence and not 

 attacking the leaves and stems, and by the larger and more finely echinulat^ 

 spores. It was probably introduced here from America, although not a 

 native of that country, for, as Clinton" says — " This is one of our most con- 

 spicuous but rather uncommon smuts. It has been introduced into this 

 country, probably from Europe." This species was first named from a speci- 

 men on Sorghum vulgare, Pers., sent by Dr. Reil from Egypt, and it was 

 afterwards found in Italy on the same host-plant. Its introduction into 

 America was probably by means of this host-plant, and then it spread to 

 maize, as it is found on both plants in the United States. 



Germination. 



The maize was taken from the field about the middle of March, just about 

 two months before maturity, and the smutted cobs were still contained within 

 their enveloping bracts. The smut spores were at once placed in tap water 

 on a microscopic slip and placed under a bell-jar, and in 17 hours several 

 had formed germinal tubes consisting of three to five cells, but usually four- 

 celled, although none had formed conidia. On germination there is an evident 

 rupture of the exospore, which is split into lobes where the germinal tube 

 protrudes. In 21 hours conidia were formed, both terminally and laterallv, 

 and the terminal conidia are the first to be formed. In one which was 

 specially observed the elongated terminal conidium was first formed, then one 

 laterally from the top of the second cell from the base, and a third just be- 

 ginning to be formed from the top of the basal cell on the opposite side. The 

 contents of the germinal tube are highly vacuolated when producing the 

 conidia, which are sometimes formed in pairs at the apex, and three lateral 

 conidia are sometimes produced together. Occasionally the germinal tube 

 may branch and the conidia may be borne direct or on elongated slender 

 sterigmata. The conidia bud in a yeast-like manner, and these sprouting 

 conidia again give rise to secondary conidia. 



Brefeld^ germinated the spores in a nutritive solution after being kept 

 for about eight years, and the sprouting conidia retain their germinating 

 power for several months, if kept drv. 



Infection. 



The mode of infection has not been determined, hut, since according to 

 Freemai and Umberger,' the formalin and hot-water treatment of the seed 

 are ineffective, the probabilities are that it does not occur through the voung 

 seedling, as in the case of Bunt, but may ho in the grain itself. These authors 

 state that the only recoininiMulation that can he made at present is to ohtaiu 



