112 ' Head Simd of Maize. 



seed from districts where it is not known to occur. It is interesting to note 

 that the " Milo " variety of Sorghum has not hitherto been attacked and 

 appears to be immune. 



American Corn Smut. 

 [Ustilago zeae (Beckm.) Unger.) 



This smut, which occurs on all parts of the maize plant, has not been 

 found in Australia, although there is another species met with which is con- 

 fined to the ear, but since this species represents one of the typical modes of 

 infection, it will be briefly discussed. 



The spores have not been found to germinate in water, but very easily in 

 a nutritive solution or on manured soil, producing the fusiform conidia. 

 These do not directly infect the plant, but give rise to sprouting conidia, and 

 very often they also put forth fungus filaments which reach the surface of 

 the culture drop, and there develop quite a number of sprouting conidia in 

 the air, similar to those produced in the fluid. These air conidia are easily 

 scattered by the wind, and play an important part in spreading infection. 



Since this smut occurs on all young and growing parts, most rarely on the 

 roots and most frequently on the stems, leaves, cobs, and tassels, it is evident 

 that we have not to do with a general infection of the plant, but 

 with a local infection, each smut-boil representing a single infec- 

 tion. Brefeld* carried out a systematic series of infection experiments, 

 infecting the various parts of the plant. He started with the young 

 seedling, as in the case of the oats, but produced only a few diseased spots, 

 and always in the neighbourhood of the collar or at the junction of root and 

 stem, while all the other parts of the plant were unaffected. Then, in other 

 parts he infected the leaves and the stem, the male and female flowers, and 

 even the young ovaries of individual flowers, always with the same result. 

 The infection was exclusively local, and it was only young and tender tissues 

 which the germinating tube could penetrate. When the fungus filaments 

 had reached maturity they broke up into spores in the usual way, with gela- 

 tinization of the membranes, and it was observed that from the period of 

 infection until the spores were produced and scattered was about three 

 weeks. 



