RATHAY'S DISEASE OF ORCHARD GRASS. 



A disease of orchard grass (Dactylis glomerata) associated with bacteria and called bac- 

 teriosis has been described by Rathay. He found it on grass growing in the shade of a 

 deciduous forest on the Vienna sandstone formation 430 meters above the sea. The locality 

 is not given, but is presumably somewhere in the vicinity of Klosterneuberg. It was not 

 found in fields or on any other grass. According to Wiesner, these plants received light only 

 one-eleventh to one-thirtieth the intensity of ordinary daylight, which resulted in a shade- 

 form with short stems and a spindling inflorescence. In 1897, 1898, and 1899, from the end 

 of May to the beginning of July, many plants of Dactylis glomerata were found having one to 

 several affected shoots. The following account is condensed from RSthay's paper. 



DESCRIPTION OF DISEASE. 

 The diseased culms were distinguished by the following peculiarities : 



(1) Dwarfing through incomplete elongation of the upper internodes. 



(2) Presence of a very viscid lemon-yellow slime consisting of bacteria which, in a layer some- 

 times as much as 0.09 mm. thick, envelops wholly or in part the uppermost leaves, the upper part of 

 the stem, and different parts of the inflorescence. All or any one of these organs may be affected. 

 Repeatedly the yellow slime was observed to occur on the outer surface of the higher internodes, as 

 well as on the outer and inner side of the leaf -sheaths enveloping them, and there were cases in which 

 an internode which bore 2 to 3 unopened, enveloping leaf -sheaths was covered with a bacterial layer, 

 while each of the enveloping leaf-sheaths was also covered with the slime on the inner as well as the 

 outer side. Thus it often happened that one could make out distinct bacterial layers separated by the 

 leaf-sheaths. 



(3) On the portions of the epidermis covered with the bacterial slime, failure of the cuticle to 

 give the characteristic brown reaction when treated first with alcoholic iodine and then with a watery 

 solution of iodine followed by concentrated sulphuric acid. 



(4) Presence soon of little yellow granules, which are found in the place of the chlorophyll bodies 

 in the cells under the diseased areas in the epidermis. 



(5) Appearance later of citron-yellow bacterial slime in the intercellular spaces of the paren- 

 chyma and in one or more vascular bundles of the parts of the stem which are covered by the bac- 

 teria. Thus far the bacteria in the leaves, both blade and sheath, have been found only in the 

 vessels of the wood, not in the intercellular spaces. 



(6) Penetration of the bacteria into the intercellular spaces of the parenchyma (Grundgewebe) 

 of the stem through the solution, in places, of the middle lamella, and the isolation of the cells thereby. 



(7) Knee-shaped bendings by means of which often one or more branches of the axis of inflores- 

 cence push out laterally from the highest leaf-sheaths which inclose the latter. This phenomenon is 

 caused, on the one hand, by the viscidity of the lemon-yellow bacterial slime on the inner side of the 

 leaf-sheath, by which slime the distorted spikes are stuck fast and, on the other hand, through the 

 elongation of the under part of the stem [see "Cobb's disease of sugar-cane," fig. 8]. 



(8) Premature drying of all the organs covered by the lemon-yellow bacterial layer. This dry- 

 ing is usually accompanied by a secondary infection with Cladosporium herbarum or a species of 

 Sporidesmium. 



It is of importance to note that no bacteria have ever been found in the subterranean 

 portions of plants of Dactylis glomerata or in any parts of normal plants. Likewise all search 

 for a similar phenomenon on other grasses (Poa nemoralis, Brachypodium silvaticum, Triti- 

 cum caninum) growing in the vicinity of the diseased Dactylis glomerata, and developing at 

 the same time, has been in vain. 



The bacterial slime reddens blue litmus paper and has no characteristic odor. The 

 existence of the slime in pure culture is suggested by the microscopic examination, which 

 shows that the bacteria composing it are morphologically alike. Cultures on various agars 

 and gelatins demonstrate, however, the presence of other organisms. In fact, on these sub- 



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