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STATE BOARD OF AGRICULTURE 



readily. They may be present in only one or a few sieve tubes in a bundle, 

 so that in examining longitudinal sections it is necessary to locate the region 

 where they are present. Once they are located they can be found in almost 

 an unbroken succession of cells along the stem or petiole. Two adjoining 

 sieve tubes are sho"^Ti in Fig. 15 with the organisms in each of them. A 

 great many of these flagellates are found in contact with the nucleus, at least 

 part of the body being in contact with the nuclear membrane. Many times 

 they have been observed actually coiled around it. Such a position of the 

 organism is shown in Fig. 16. This intimate contact with the nucleus is 



Fig. 17. Photomicrograph of longitudinal section through potato petiole tissue from leaf-roll plant, 

 showing characteristic trypanosome-like organism that is associated with this disease lying 

 in a sieve tube. X 1500. 



A. Sieve plate. 



B. Trypanosome. 



C. Sieve tube. 



D. Cell nucleus. 



more pronounced and more common than has been observed with the or- 

 ganisms found in tomato and bean mosaic. Many of them, however, are 

 free within the host cell and are found at various places in the cell. Their 

 position is nearly always parallel with the long axis of the cell, although 

 smaller forms are occasionally seen lying obliquely. A large organism is 



