I 'sfi/di'O. 



147 



This smut is vorv common ou cultivated oats, and occurs in all the States. 

 It is usually cautiued to the iutloresceiice, but Clinton^ records it as occurriiio; 

 ou the leaves iu rare cases, and Japp^ found it in the anthers. It has been 

 found on th? wild oat in California, and occasionally on the same host in 

 Victoria.* 



Spore jormalion. — If cross-sections are made of an affected ovary in the 

 3^oung condition, the spores are seen forming around a central core of tissue, 

 the youngest and colourless spores being innermost. They are also formed 

 in isolated groups which may eventually run together. In these individual 

 groups there is a Cintractia-like formation of spores, the very minute colour- 

 less spores being towards the centre, and the dark-coloured mature spores 

 collected towards the circumference. The spores, however, are not agglu- 

 tinated together to form that cheese-like consistency which is characteristic 

 of Cintractia. 



Germination. — Fi-esh material was taken from the field and the spores 

 germinated freely both in water and nutritive solution. Germination takes 

 place in a few hours, and a promycelium is produced, divided into segments 

 by three or four transverse septa. Each of the segments generally bears a 

 conidium, the top one producing it at the apex. The conidia may either 

 fall away or remain attached, and give rise at their free end to a secondary 

 conidium. The conidia when moist develop further, and may either directly 

 put forth a slender germ-tube or two o" them adjoining may become con- 

 nected, and the one reinforced by the protoplasm of the other gives rise to 

 a germ-tube. When spores are cultivated in a nutritive solution instead 

 of water, an important difference arises. The conidia are formed as before, 

 but they begin to sprout on their own account after the manner of yeast, 

 and form sprouting conidia. In liquid manure this process of sprouting can 

 go on indefinitely, and Brefeld maintained it over a year by keeping up the 

 food supply. It must be remembered that this result was obtained with 

 " pure cultures," but under natural conditions it is highly probable that the 

 process would be checked, if not entirely hindered, by the development of 

 other organisms. Spores have germinated after being kept for seven and 

 a half years, and thus, in the staying power of the spores and in the immense 

 numbers of sprouting conidia produced, this smut possesses unlimited powers 

 of spreading. 



(Plates VIII., IX., XXVI.) 



Ilordmm. 

 2. Ustilago hordei (Pers.) Kell. & Sw. 



Kellerman and Swingle, Ann. Kep. Kans. Aur. Exp. Sta., p. 268 



(1890). 

 Sacc. Syll. IX., p. 28:3 (1891). 

 Ustilago segetum (Bull.) Dittm. 

 U. jensenii Rostr. 



Sori in spikelets, forming a black compact spore mass, enclosed in the 

 glumes and covered rathci' permanently bv the unbroken walls of 

 the ovary, hence called coxcrcd smut of barley. Spores remain 

 adherent, being bound toiicllici' bv ])atclies of tissue in interior of 

 spikelet. 



* The wild oat can be infected witli smut from the tame oat, and the tame oat with smut from the 

 will oat, so that the same species occurs on both. The form on tlie oat grass resembles the tvpe in 

 stru-ture and germination, and the fact that the mycelium is perennial does not entitle it to sijeciflc 

 distinction. Cross infection with the oat will be tried during tlie coming season. 



