EXPERIMENT STATION BULLETINS. 433 



nation of juice expressed from diseased petioles. The first method is the 

 most satisfactory. Petioles from plants showing severe mosaic symptoms 

 were used and longitudinal sections cut through the phloem after splitting 

 the petiole with a Gillette razor blade. These sections were mounted imme-^ 

 diately in boiled water and examined under the high-power dry lenses, the 

 illummation being reduced to a minimum necessary to make out plant struc- 

 tures. The flagellates were seen in the sieve tubes in an actively motile 

 state. 'In stained as well as living material rarely is more than one individual 

 found in a cell, and some cells contain none, so that it is necessary to find a 

 favorable location on the slide where the flagellates are present. The body 

 of the organism is seen in a rapidly whirling motion, disappearing from sight 

 in the depths of the cells only to reappear again, turning over and over but 

 changing its relative position but slightly in the cell. Only the body of the 

 flagellate can be seen, as the flagella are not visible under these conditions. 



For examining the organisms with dark-field condenser short pieces of 

 petiole were laid on clean plate glass and the juice rolled out by means of a 

 photographer's hard-rubber roller. Hanging drops were examined under oil- 

 immersion lenses with arc-light illumination. An occasional flagellate was 

 seen to flash across the field but apparently so few organisms are expressed in 

 the relatively large amount of juice that they are not easily located in this 

 way. Thin longitudinal sections are more satisfactory for observing the 

 motility. 



The size of the flagellates is very variable, as would be expected where they 

 are present in various stages of development. Measurements of type 1, the 

 elongated biflagellate forms, which constitute the majority of individuals, 

 are given here. These measurements are based on fixed and stained material 

 and, therefore, will be slightly less than the actual size of the organisms in a 

 living state. A filar micrometer was used in making the measurements and 

 the size of the body determined separately from the flagella. The following 

 table shows the variation in 50 individuals measured in consecutive order as 

 they occurred in the sieve cells: 



Longest individual 18X2.8 microns. 



Shortest individual 5X0.3 microns. 



Broadest individual 13.9 X 3.9 microns. 



Slenderest individual 11.3 X 0.3 microns. 



Longest flagellum 18 microns. 



Shortest flagellum 7.2 microns. 



Average length of organism 13.5 microns. 



The generic position of these flagellates does not coincide with that of any 

 of the known protozoa. Before fixing their systematic position decision must 

 first be made as to which form represents the adult type. Individuals with a 

 flagellum attached to each end of the body are most common and appear to 

 represent the adult form, and if generic classification is based on their mor- 

 phology, then it will be necessary to erect a new genus to include them, as 

 they differ from those genera of protozoa at present known which possess a 

 single flagellum attached to each pole. Mention should be made here of the 

 possible relationship but not generic identity of these organisms to those 

 found in the latex of Euphorbiaceous and Asclepiadaceous plants and be- 

 longing to the genus Leptomonas (6). The bean organism is distinctly a 

 difl"erent type, however, arid its exact position will necessitate further study. 



