Aug. xi, 1923 
Irish Potato Foliage Degeneration Diseases 
265 
tubers with scattered sprouts, all apparently of equal vigor, the plants 
from the several seed pieces are approximately uniform. It seems to be 
true that a degree of apical dominance is shown in the material studied, 
in the large size and yields of hills from apical buds. The fact that 
should be emphasized, however, is that this dominance is not an index 
of freedom either from mosaic or leaf roll. 
The writer’s conclusion with reference to the bearing of apical dom¬ 
inance upon the present problem is that the appearance of the sprouts 
as to normal thickness, branching, etc., is a better index of the healthy 
or diseased condition of the tuber and of the resulting plants than the 
distribution of the sprouts on the tuber; and further, that the data so 
far collected fails to support any consistent correlation between the 
distribution of sprouts on the tubers in storage and mosaic of the result¬ 
ing plants. 
SUMMARY 
(1) In instances both of serious mosaic and serious leafroll infection, 
germination of the seed pieces and growth of the shoots are markedly 
retarded. 
(2) (a) In the strains of Green Mountain potatoes under observation 
in these investigations the same plants frequently exhibited both mosaic 
and leafroll infection. 
(6) All the data secured support the thesis that there is uniformity 
as to condition of health or disease in all the plants from a single tuber 
and also in all the tubers from a single hill. 
(3) Marked variation in the progressive development of mosaic 
infection with the suggestion of differing strains of mosaic virus were 
indicated in the germination of tubers of known ancestry and in the 
observation of several successive generations of plants from known 
sources. 
(4) (a) Spindling-sprout of the tubers is shown to be, in the varieties 
of potatoes studied, a consistent symptom of leafroll, but not of mosaic. 
(6) Net-necrosis, of the phloem-necrosis type, is correlated in the 
tubers with spindliness of sprout and seems to be a consistent symptom 
of leafroll. The necrosis symptoms are not persistent in the progeny 
tubers. 
(c) Yields of plants from spindling-sprout tubers were much reduced 
in comparison with those of plants from tubers with normal sprouts, 
and hills exhibiting extreme leafroll yielded far less than those with 
mild leafroll symptoms. 
(5) Apical dominance in sprouting which has been held to be an 
indication of vigor in tubers was found to be associated both with the 
development of mosaic in the foliage and with a healthy condition of 
plants, and conversely, the lack of apical dominance was associated 
with the production of healthy as well as mosaic hills. 
LITERATURE CITED 
(1) Appel, Otto. 
1915. LEAF ROLL DISEASES of the potato. In Phytopathology, v. 5, p. 139-148. 
(2) ApplEman, Charles O. 
1914. BIOCHEMICAL AND PHYSIOLOGICAL STUDY OF THE REST PERIOD IN THE 
TUBERS OF SOLANUM TUBEROSUM. Md. Agr. Exp. Sta. Bill. 183, p. 
181-226, 17 fig. Literature cited, p. 225-226. 
(3)- 
1918 
. PHYSIOLOGICAL BASIS FOR THE PREPARATION OF POTATOES FOR SEED. 
Md. Agr. Exp. Sta. Bui. 212, p. 79-102, 11 fig. 
