rathay's disease oe orchard grass. 157 



COMMENT. 



This interesting paper leaves many particulars undetermined. The disease as described 

 has some points of similarity to Cobb's disease of sugar-cane and to Stewart's disease of 

 sweet corn. If it is like the latter, then we may suppose that infection occurs earlier in the 

 season at the base of the plant and that Rathay was in error in supposing the occlusion of 

 the vascular system of the stem to be a secondary or late infection. If, on the contrary, as 

 he states, the organism attacks the parts first observed by him to be diseased and makes its 

 way across tissues from the surface to the interior, it would seem to be like Burrill's disease 

 of broom corn and then we might suspect aphides or similar insects of being carriers of the 

 disease. 



The failure of cultures on agar and gelatin is probably attributable to defective tech- 

 nique, very viscid growths, such as Rathay describes, not lending themselves readily to 

 plate cultures without some preliminary rubbing up in water or bouillon (see B. trachei- 

 philus, vol. II, pp. 287, 294). It is probable, as he believes, that the great mass of the yellow 

 slime on the plants was an unmixed or nearly unmixed growth. It is not likely that the wrong 

 organism was isolated, and it is probable that if young cultures had been inserted into young, 

 growing stems and leaves by needle-pricks successful infections might have been obtained. 



The last paragraph of the paper promises a full account of the disease and of the organ- 

 ism later on, the same to be properly illustrated. Death, however, cut short the distin- 

 guished author's labors, and, so far as known to the writer, nothing has since been published 

 on this interesting disease. 



Through the courtesy of Prof. Dr. Julius Wiesner, of Vienna, I learn that this disease 

 occurs on the Kahlenberg between Stephaniewarte and the track of the Kahlenberg- 

 (Zahnrad-) Bahn, i. c, near Vienna. Rathay's material is preserved in the Lehr Anstalt 

 fur Wein- und Obstbau at Klosterneuberg. 



PERSONAL OBSERVATIONS. 



After the above comments were in type the writer received from Dr. F. K^lpin Ravn, 

 of Copenhagen, heads of Dactylis glomerate (collected in Denmark), attacked by a bacterial 

 disease which appears to be identical with that described by Rathay. Dr. Ravn's note is 

 as follows : 



As samples without value I send you some specimens of Dactylis glomerata, infected by bacteria. 

 The disease is reported in Kirchner: Krankheiten und Beschadigungen, 2 Aufl., p. 163, but bas- 

 so far as I know not been studied more closely. Last summer my assistant, Mr. F. Lind, dis- 

 covered the disease in this country and found that it is widely spread and is of some significance for 

 the growing of seed of Dactylis. Mr. Lind continues his field studies, but we would be much obliged 

 to you if you might have time to report to us your opinion as to the identity of the bacterium after 

 cultural characters and comparison with others. 



The heads of these plants are dwarfed, distorted, and gummy-yellow from the presence 

 of enormous masses of surface bacteria, and often imprisoned within the leaf-sheaths which 

 are stuck together (fig. 71a). The glumes, which are badly attacked, are lemon yellow 

 or water-soaked, and the sheaths and stems are also involved more or less. On some spike- 

 lets only a portion of the glumes are attacked and these not in all parts. (For an early 

 and late stage of the disease on the spikelets see plate 41 , figs. 9 and 10.) The yellow slime 

 is also abundant between the upper unfolded leaves and the stem (B, B of fig. 71c?). This 

 yellow slime reddens blue litmus paper. 



Microtome sections show extensive occupation of the floral organs (pi. 1 1 a) . The bac- 

 teria are present mostly between and surrounding these organs, as in the gum-bud disease 

 of carnations (see this monograph, vol. II, fig. 4). In many cases they have been seen 

 occupying intercellular spaces (figs. 710, 71/), and more rarely vessels. 



The organism most abundant on these plants is a yellow, non-motile, non-sporiferous 

 schizomycete, which so far has refused to grow readily on any sort of agar, but which grows 



