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STATE BOARD OF AGRICULTURE 



being very long and sinuous, others almost straight, and still others compara- 

 tively short and broad — that the morphology of the species will require 

 extensive investigation. Such polymorphism, however, as was shown by the 

 bean flagellates has not been found in these organisms associated with tomato 

 mosaic. 



In the slides stained with haematoxylin only a very few of the organisms 

 have been found with the nucleus sufficiently stained to make it visible. In 

 some of the preparations where destaining was carried far enough it can be 

 made out centrally located in the body, while other deep-staining granules, 

 apparently kinetonuclei, are visible near the extremities. Some portions of 

 the organisms are stained more deeply than others but for a detailed study of 

 structure it will be necessary to develop differential stains or modify some of 

 the present protozoan solutions so as to adapt them to plant material. Much 

 more desirable would be the growing of these flagellates in pure culture and 

 staining them in the absence of the host-plant tissues. 



Fig. 15. Longitudinal section through the phloem of a potato plant affe-'ei with leaf-roll. Two elon- 

 gated, slender protozoan organisms are shown in adjoining sieve tubes. X 650. 



A. Protozoan organisms. 



B. Sieve tube. . . 



C. Sieve plate. 



D. Cell nucleus. 



