46 
Journal of Agricultural Research 
Vol. XXV. No. » 
called a hill lot. Hill lots from the same tuber unit are the beginning of 
a tuber-unit strain. A hill lot usually is planted SO that it consists of 
consecutive undivided tuber units, in order that comparison between 
tubers may be made more easily. 
TRANSMISSION AND DIAGNOSIS IN THE GREEN MOUNTAIN VARIETY 
A given degeneration disease often differs with the variety of potatoes, 
so that the data first presented will be limited to the variety with which 
the writers are most familiar. In this variety, the Green Mountain, 
several diseases have been distinguished, occurring both singly and in 
combinations. They will be considered first separately and then com¬ 
paratively, with final consideration of the question of combinations. 
MIED MOSAIC 
Mosaic of potatoes was first described in the literature by W. A. Orton 
(j2 } p. 42; 2g y p . 59) although Quanjer claims to be the first to dis¬ 
tinguish it (59, p. 128 ): 
Gradually I learned to distinguish the leaf-roll type, and another type which re¬ 
minded me of the mosaic disease of tobacco.Aiterwards Danish and American 
investigators also began to distinguish mosaic. 
The term “mosaic” will be used here as covering several types of 
diseases all characterized in common by mottling and wrinkling. The 
term “mild mosaic” has been used by Tolaas (49, p. 10) and is now used 
by the writers as equivalent to the slight, slight plus, and, in part at 
least, the medium stages of mosaic as previously described by them 
(40,'p. 316). The characteristic symptoms consist of slight dwarfing, 
distinct mottling, wrinkling, and some ruffling (PI. 1, B, 1, C,2). As 
will be shown later, it is more easily transmitted than leaf roll and is less 
easily transmitted than rugose mosaic and streak. The tuber symptoms 
are a general average reduction in size. 
contact inoculations 
As reported previously (40, p. 319), tuber-graft inoculation may result 
in infection with current-season symptoms. Stalk grafts may do the 
same (45, p . 231-33; 40 , p. 319). Temporary contact of healthy and 
mosaic seed pieces all cut with the same knife did not cause appreciable 
infection (40,/). 332-33). Contact of uncut tubers in storage probably 
results in no transmission. Several stocks with a small percentage of 
mosaic have been used to furnish seed for greenhouse experiments early 
in the winter and also for field experiments after winter storage, but did 
not have a higher percentage of incidence in the field after the longer 
period of contact of the tubers in storage. 
Contact of healthy and mosaic shoots was not followed by infection 
in greenhouse experiments (45, p. 264-63) except after aphids had fed 
upon these shoots. 
Contact of both shoots and roots in the greenhouse (40, p. 333) was 
not followed, during three months of active growth subsequent to 
establishment of contact, by any mosaic symptoms. This was in marked 
contrast with results in a contemporary experiment wherein plants 
that started to grow 2 weeks later and that were harvested at the same 
