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STATE BOARD OF AGRICULTURE 



curs, separating the organism into two equal daughter flagellates. These 

 stages of division are shown in Figures 5 and 6. It is very likely that other 

 modes of division occur in the life history of this organism. No form of 

 division which produces the very small flagellates, some less than 0.3 micron 

 in width, has been observed. Whether the large, elongated forms represent the 

 adult type, which would be the basic form for generic classification, or whether 

 some of the other types are the real adults, are questions which can not yet be 

 answered. The form in which the organism is inoculated into healthy plants 



Fig. 7. Photomicrograph of longitudinal section through subepidermal tissue of bean plant affected 

 with mosaic. Note that the chloroplasts are filled with small, elongated, deeply-stained 

 organisms. X 1500. 



A. Chloroplasts filled with the organisms. 



by the aphids which transmit the disease, and the question of whether or 

 not these insects are merely accidental carriers of infectious material or actual 

 hosts for some form in the life cycle of the flagellates are questions whose 

 answer is merely speculative at present. 



The migration of these flagellates from cell to cell has not been observed. 

 The small forms might readily pass through the perforations in the sieve 

 plates and thus become distributed throughout the sieve tubes. Likewise 

 the very small flagellates once introduced into the parenchyma cells could 

 possibly pass from cell to cell through the cytoplasmic connections. Fur- 

 ther study is necessary for clarification of these points. 



The organisms have been demonstrated in living material by means of 

 thin longitudinal sections through the phloem and also by dark field illumi- 



