T22 Life Histories of Various Grass Smuts. 



The monetary loss from this smut is considerable, since the crop is so 

 valuable. Amber cane, when it is grown for seed, may sometimes be worth 

 £25 to £30 per acre, so that the loss is serious enough to render preventive 

 treatment desirable. 



Distribution. 



It occurs in Southern Europe, Asia, Africa, and America, as well as in 

 Australia. It was brought to the United States through imported seed, and, 

 no doubt, it was also introduced here in the same way. I have examined 

 seed of amber cane and sugar sorghum obtained from the best seedsmen, and 

 in every instance the spores of the smut were present, even although it ap- 

 peared to be quite clean, as from the mode of hand-picking the seed and 

 winnowing, none of the smut bodies were found. Is there any wonder, then, 

 that the smut, from being a negligible quantity, should be gradually on the 

 increase, when the spores are regularly sown with the seed, without any 

 treatment ? 



Germination. 



The spores germinate readily in water. Fresh spores were taken in Feb- 

 ruary, and in twelve hours there was vigorous germination. They retain 

 their germinating power for a number of years, and De Bary states that 

 Liebenberg germinated them after being in the herbarium for six and a-half 

 years. 



The germination has been described by Brefeld, Clinton, Norton, and 

 others. The spore puts forth a promycelium, which divides into three or 

 four cells by transverse septa. Quite a feature of the promycelium is the 

 formation of the so-called buckle or knee-joints. A short out-growth arises 

 at the end of one or more cells, and this bends over and unites with the ad- 

 joining end of the next cell. From these protuberances or from the end of 

 the promycelium slender filaments of varying length grow out, called by 

 Clinton infection threads, on account of their supposed function. Conidia 

 are generally produced either from the tip of the promycelium or at the apex 

 of the cells and readily fall away from their connexion. 



In a nutrient solution the germination was more luxuriant and the for- 

 mation of conidia was increased. 



Infection. 



This takes place in the seedling stage, and may either occur by means of 

 infection threads from the promycelium itself or from conidia. These threads 

 must reach the growing tip of the plant in order to infect successfully, and 

 that is only possible when the cells are young and tender. Whenever the 

 young plant appears above ground it is then proof against infection. 



Spore Formation. 



A cross-section of a young infected ovary shows a central core of plant 

 tissue or columella, a firm outer wall, and the spores between. The outer 

 membrane is composed of a more or less distinct epidermis with a layer of 

 fungus cells beneath, which may attain a thickness of 40 //. The spores are 

 fully formed on the outside nearest the fungus layer and gradually become 

 immature towards the centre. If the spores are traced from the columella 

 they begin to be formed just outside the fibro- vascular bundles. The fungus 

 filaments seem to have gelatinized their walls, and the protoplasmic contents 



