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 appearance. 
Four days later the yellowish spots were more pronounced and 
appeared on about two-thirds of the leaflets. The very youngest 
leaves were also conspicuously pale, with a sickly yellow color. 
In this early stage the mottled effect is not perceptible, but it 
becomes 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 
yellow spots, which appear at any place on the leaf. See 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 
hypertrophies were lacking. The disease appeared spontaneously 
without pruning 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 
plants came from New York. 
