154 The Ohio Naturalist. [Vol. XIII, No. 8, 



the purpose of growing plants for breeding experiments. The 

 writer has found no extensive description of mosaic disease on the 

 potato in the literature, but it was reported by Orton (1913) as 

 occurring in Germany and Maine. 



The first symptoms were noticed on a plant which had reached 

 a height of approximately eighteen inches. When first observed 

 the plant appeared thrifty in every respect, except that the 

 immature leaves had a slightly pale and mottled appearftnce. 

 Four days later the yellowish spots were more pronounced and 

 appeared on about two-thirds of the leaflets. The very yotuigest 

 leaves were also conspicuously pale, with a sickly yellow color. 

 In this early stage the mottled effect is not perceptible, but it 

 becoines noticeable as the leaflets age. Those having practically 

 reached their full development, occasionally showed a slight 

 abnormality in shape or an uneven surface. See text Fig. 1. 

 The mottled effect consists of irregular, greenish-yellow or pale 

 3^ellow spots, which appear at any place on the leaf. vSee plate VII. 

 As in tobacco and tomato mosaic, the yellow spots are localized 

 in the tissue between the veins, which have a conspicuous border 

 of dark green tissue. If such leaflets are sprinkled or submerged 

 in water, the color differentiation is greatly intensified. In the 

 majority of leaflets the green areas developed more rapidly than 

 the yellow as usual in this disease. Such differences in growth 

 cause a somewhat irregular surface. 



Upon examination, it is to be observed that the hairs on the 

 upper surface of the leaf are much closer together in the yellow 

 areas than in the normal or in the green areas. It appears that 

 the hairs develop as usual while the leaf is very young, but that 

 there is less than the normal expansion of the leaf surface between 

 them, so that they are left standing close together, giving the 

 leaf a striking and peculiar appearance. The surface of a cal- 

 icoed leaflet when examined under a hand lens, shows that the 

 dark green areas are somewhat elevated, while the yellow areas 

 are slightly depressed, giving the surface an uneven appearance. 

 No peculiarities could be seen upon the stalks or petioles and 

 hypertrojihies were lacking. The disease appeared spontaneously 

 without ])runing or other mutilation or artificial stimulation, 

 which is said to be sometimes responsible for the production of 

 such deformities in the potato (Woods 1902), as well as in other 

 hosts. The writer has not observed this trouble on potatoes 

 growing in the field, but intends conducting experiments later. 

 It might be stated that the tubers which produced these diseased 

 plant'^ came from New York. 



