EXPERIMENT STATION BULLETINS. 



441 



Potato Leaf -Roll 



The study of material from potato plants affected with leaf-roll has been 

 carried out in the same way as for bean and tomato mosaic. The plants were 

 first carefully exammed to exclude if possible any that might also be affected 

 with mosaic. The plants used for this study were taken from a small patch 

 of potatoes where no mosaic was found. They showed unmistakable symp- 

 toms of leaf-roll, the lower leaves being uprolled, rigid, brittle, and much 

 thickened, while the entire plant was stunted in growth. Pieces of stem and 



Fia. 16. Photomicrograph of a protozoan coiled around a sieve tube nucleus in a potato plant affected 

 with leaf-roll. X 1500. 



A. Trypanosome. 



B. Nucleus. 



C. Sieve tube. 



D. Elongated protozoan partially out of focus. 



petiole from near the top of the plant were cut and fixed. Some difficulty 

 was experienced in cutting good sections with phloem and xylem tissue intact. 

 Lying in the sieve tubes of petioles and stems, long, trypanosome-like 

 organisms were found which stained in much the same maimer as the bean and 

 tomato organisms. They vary as much as do the types found in tomato mo- 

 saic plants, but are, nevertheless, characteristic and constant for this disease. 

 On account of their distribution in the plant and the tendency to distribute 

 themselves along only certain of the sieve tubes they are not always found 



