PLATE 29 



A. — Mosaic of potato transmitted by aphids. 142a, infected plant, Green Mountain 

 variety. Plant developed beside a badly mosaic plant, thus allowing free infection 

 by the aphids. Upper leaves distinctly mottled and crinkled. Lower leaves without 

 mottling. 142b, healthy plant from same tuber as 142a. Greenhouse, Washington, 

 D. C, March 14, 1918. 



B. — Two plants from the same tuber treated alike, except that about 200 aphids 

 were introduced upon one when it was 2 inches high. Photographed 46 days after 

 the introduction of aphids and 26 days after the first signs of mosaic were shown. 

 Greenhouse, Orono, Me., April, 1919. 



