1923] 



DTJGGAR & KARRER — NATURE OF MOSAIC DISEASE PARTICLES 199 



is that essentially all of these may be paralleled in perfectly 

 healthy tissue. Moreover, the relations of these bodies seem in 

 no way to suggest flagellates that may be normal to the tissues, 

 whether diseased or healthy. From our studies we are convinced 

 that these "flagellates" are made up of several factors, and while 

 we have not attempted a careful micro-chemical examination, 

 nor made a complete study of the developing tissues, such possi- 

 bilities as the following may be noted : elongated masses of gummy 

 material long known to be characteristic of certain sieve tissues; 

 cytoplasmic aggregations or areas of contraction possibly associ- 

 ated with disintegrating plastids; elongate, accessory, and perhaps 

 disintegrating nuclei; and homogeneous aggregates of unknown 

 origin, possibly of waxy nature. 



The importance of the problem justifies the feeling that a 

 complete reinvestigation of these cell phenomena is being pursued 

 by many others, and that out of it may come some compensating 

 observations that will throw light rather than shadow on the 

 nature of the mosaic diseases. 1 



ULTRAFILTRATION EXPERIMENTS 



The fact so frequently confirmed that the agency of mosaic 

 disease passes freely through the pores of the average Berkefeld 

 or Chamberland filter did not establish, prior to 1921, the size of 

 the infective agency further than to indicate that it is considerably 

 less than that of the usual plant or animal pathogen. It sufficed 

 merely to relate the agency to filterable organisms. In order 

 ultimately to determine more accurately the relations of this 

 agency it seemed essential to make a detailed study of its size 

 relations. This was done by the present writers (Duggar and 

 Karrer, ? 21), and reference to this work is a necessary preliminary 

 to the further results which will be reported and to the theoretical 

 considerations which we wish to present. 



The work referred to consisted first in securing graded series 

 of ultrafilters, some of which should permit the infective particles 

 to pass freely (as shown by the infectiousness of the juice) and 



1 Since the oral presentation of this paper, much additional light has been thrown 

 upon the distribution and relations of these abnormal bodies described by Nelson, 

 and similar structures, in a series of papers published in Phytopathology, Vol. 13, 

 No. 7, 1923, by the following authors: (1) Kotila and Coons; (2) Doolittle and 

 McKinney; (3) Kofoid, Severin, and Swezy; and (4) Bailey. 



