THE FUNGI WHICH CAUSE PLANT DISEASE 23 



agree in the following particulars: They are yellow rod-shaped 

 organisms of medium size, straight or slightly crooked with 

 rounded ends. The segments multiply by fission, after elongation. 

 They are generally less than 1 /i in diameter. The segments 

 occur singly, in pairs or in fours joined end to end, or in clumpy 

 masses of variable size (zooglceae), more rarely they are united 

 into long chains or into filaments in which no septa are visible. 

 Endospores have not been observed. The segments are motile by 

 means of one polar flagellum which is generally several times as 

 long as the rod, and may be wavy or straight when stained. The 

 species grow readily on all of the ordinary culture media, but so 

 far as is definitely known all are strictly aerobic. None are gas 

 producers. They do not reduce nitrates to nitrites. The yellow 

 color appears to be a lipochrome and in the different species varies 

 from deep orange and buff-yellow, through pure chrome and 

 canary-yellow, to primrose-yellow and paler tints. 



Ps. seruginosus Del. possibly identical with Ps. flourescens- 

 putridus Fliigge is the cause of a leaf and stem disease of tobacco 

 in France.^^ 



Ps. avenae Manns, (Group number 111.2223032.) A short rod 

 with round ends, 0.5 to 1 /i x 1 to 2 ii. Actively motile, generally 

 by one polar flagellum, occasionally by two or three. Gram 

 negative. What seem to be endo- 

 spores are found in old cultures. On 

 agar stroke, growth very slow, fili- 

 form, rather fiat, glistening; margin 

 smooth, opaque to opalescent; non- 

 chromogenic. Liquefaction occurs on 

 gelatine in seven to twelve days. 

 Broth is slowly clouded. Agar colo- 

 nies, amorphous, round with surface 

 smooth, edges entire. No gas in 

 dextrose, saccharose, lactose, maltose, Fig. lo.— Ps^^nae. After 

 or glycerine. Ammonia and indol 



not formed. Nitrates reduced to nitrites. T. D. P. 10 min., 

 60°, Opt. 20° to 30°. 



This organism was isolated and described by Marms in 1909,'* 

 as the cause of a serious oat blight. Inoculations with it alone by 



