Potato Mosaic. 161 



upward rolling of the leaves with dwarfing and a paleness or 

 yellowing not localized in scattered spots. Moreover, this mal- 

 ady, together with certain other inheritable abnormalities of the 

 leaves that may be phases of mosaic, probably requires the same 

 practical treatment as does mosaic. 



In a field with many mosaic plants the color of the mass of 

 plants is lighter green, the rows are more ragged, the plants are 

 not so robust or tall, and in case of dry weather yellowing and 

 dying occurs earlier than with healthy stock of the same variety. 

 See Figs. 29 and 30. 



Other Effects of the Disease. 



A limited number of chemical tests 6 have indicated that 

 mosaic is accompanied by an increase in the amount of sugars 

 in the leaves and by a decrease in the amount of starch. Similar 

 tests may eventually disclose the same differences in the tubers, 

 but at present no way is known for distinguishing healthy dor- 

 mant tubers from those which are transmitting the disease. The 

 latter germinate as well as the former do. The blossoming stage 

 is reached as soon by diseased plants as by healthy. Vegetative 

 reproduction is modified so that the disease decreases the yield 

 of tubers. 



A number of tests have been made by various writers 7 com- 

 paring groups of diseased hills with groups of healthy ones re- 

 garding the yield of potatoes. These show that the disease in 

 such conditions reduces the yield. They thus agree with the 

 results of similar studies made in Maine, wherein larger num- 

 bers of hills were used. 



G Schultz, E. S., Folsom, D., Hildebrandt, F. M., and Hawkins, L. A. 

 Op. cit. 



'Anonymous. Mosaic disease as a factor influencing yield. Potato 

 Magazine 2 5 :11, 27. 1919. 



Barrus, M. F. Potato-mosaic and certified seed. Potato Magazine 

 1 4 :13-14. 1918. 



Murphy, P. A. The mosaic disease of potatoes. Agric. Gaz. Can- 

 ada 4:345-349. Illus. 1917. 



Orton, W. A. Op. cit. 



Parker, R. C. Testing seed potatoes on Long Island. Potato Mag- 

 azine 2 3 :8, 22-23; 2 4 :19, 27-28. 1919. 



Wortley, E. J. The transmission of potato mosaic through the tu- 

 ber. Science n. s. 42:460-461. 1915. 



