Lije Histories of Various Grass Simits. 121 



CHAPTER XX. 



Life-Histories of various Grass Smuts. 



Only a few of the smuts occurring on various grasses of economic im- 

 portance will be noticed here, in which the mode of germination of the spores 

 and infection are known, and a more or less detailed account given of their 

 life-history. There are still a number awaiting further investigation, and 

 among our native grasses practically nothing has been done in the way of 

 preventing the spread of the smuts attacking them, which are sometimes 

 very destructive. 



1. Grain Smut of Sorghum. 



(Cintracfia sorghi-vulgaris (Tul.) Clint.) 



There are two kinds of smut which occur on sorghum, the Grain smut, so 

 called because it confines itself chiefly to the individual grains, and the Head 

 smut, because it converts the whole head, just as it emerges from the upper 

 leaf into one large smutty mass. The Head smut of maize has already been 

 described, and the same fungus which causes it is also found on sorghum, but 

 not hitherto in Australia. It is the Grain smut which has been found here 

 on broom corn, amber cane, and sugar sorghum, and wherever it occurred 

 was very destructive. The cultivated sorghums are placed under Andro- 

 pogon sorghum, Brot., by Hackel, of which there are a number of varieties, 

 such as broom corn, amber cane, and sugar sorghum, the latter variety being 

 usually called Sorghum saccharatum, Pers. 



Effects and Losses. 



The effects of this smut upon the host-plant is very noticeable in pre- 

 venting the formation of seed. The seed is replaced by an enlarged body of 

 a dirty white or brownish colour, splitting irregularly at the top and exposing 

 a mass of dark-brown spores. In a crop of sugar sorghum examined in 

 March there were about 14 per cent, of the plants affected (1 in every 7), 

 while amber cane grown in the same field was only slightly affected. 



The smutted ears or panicles are readily recognised in the field, from the 

 grains being replaced by a horn-like projection of a dirty white or brownish 

 colour. The individual smut bodies are not only considerably elongated, but 

 usually somewhat stouter than the normal healthy grains (Plate XIV.). The 

 ear may be attacked by the smut even while still green, and a portion of it 

 only in flower. Occasionally there may be a few clean grains on an other- 

 wise smutty ear. In the case of broom corn the loss is not so serious as where 

 the sorghum is raised for seed. Nevertheless, the brush of an infected plant 

 is of an inferior grade, and almost worthless. In healthy broom corn the 

 rays are uniform in thickness and length, and all spring from nearly the same 

 point, but in infected plants the rays are of unequal length, and arise from 

 an elongated and thickened central axis. The number of large rays, too, are 

 always less, so that the commercial value of the brush is lessened. One 

 prominent grower stated that most of the heads that have smut on them are 

 of no account. 



