444 STATE BOARD OF AGRICULTURE 



The size of these organisms is verj^ variable. The measurements given 

 in the table below show the limits of variation that have been observed : 



Longest form measured 35 microns 



Shortest form measured 11.3 m'crons 



Broadest form measured 3.0 m'crons 



Slenderest form measured 0.9 m"cron 



Average all measurements 23.6 X 1.8 microns 



Smaller individuals than those given in the table above have been seen, but 

 on account of their position in the cell have not been measured. Some are 

 coiled around the nucleus, others occupy positions such that a portion of the 

 body is obscured, so that the measurements given in the table, while repre- 

 sentative of a majority of individuals, can not be said to show the extreme 

 variation in size. Further study and measurements of a large number of 

 individuals must be made before any definite conclusions concerning these 

 points can be made. 



For a study of healthy tissues sections were made from plants that showed 

 no symptoms of leaf-roll. No organisms have been found in the sieve tubes 

 of these plants in all the slides examined. From all the evidence gathered in 

 this study of diseased and healthy material it seem safe to conclude that these 

 organisms occur in the sieve tubes of diseased plants but are absent from these 

 structures in healthy ones. . 



Xaftirr of the Organisms 



From the study that has been made of the organisms associated with the 

 diseases investigated there seems little doubt of their protozoan nature. 

 Their simple unicellular structure, possession of flagella and undulating 

 membranes, the presence of kinetonuclei and other characteristics that coin- 

 cide with the peculiarities of the protozoa, seems sufficient proof of the true 

 nature of the forms found in the phloem tissues of plants affected with mosaic 

 and similar diseases. The systematic position of these organisms is a ques- 

 tion requiring more detailed study. While not final, the evidence now seems 

 to warrant a few conclusions, which may be considered tentative until fur- 

 ther study shall place these forms in their proper generic position. The 

 biflagellates associated with bean and clover mosaic are apparently a new 

 form, since no type of protozoan similar to it has been described. It differs 

 from other probably closely related types, like Leptomonas, in the arrange- 

 ment of the flagella. The Leptomonas organisms found in the latex of 

 Euphorbiaceous and Asclepiadaceous plants are typical members of that 

 genus with a single polar flagellum, while the bean organism has one flagellum 

 attached to each pole, a characteristic that is constant in all the material 

 examined. 



The great resemblance of the organisms found in mosaic tomato plants to 

 trypanosomes is unmistakable. While there is great variation in the mor- 

 phology of various individuals the general characteristics are more nearly 

 like those of trypanosomes than any other form. The great polymorphism 

 shown by the different species included within the broad limits of the genus 

 Trypanosoma admits forms which might possibly belong in other subdivisions 

 that have been proposed for this genus. They have, however, not been 

 generally accepted by protozoologists. Certain details of structure have 

 not been demonstrated with the stains that have been used, so that for the 



