56 
Journal of Agricultural Research 
VoL XXV, No. » 
In field 34, Table XXVIII, the spread from diseased rows was such 
that samples from the first adjacent healthy row gave progeny with 
6o per cent of the hills diseased, while six samples from more distant 
rows gave progeny with only io per cent diseased. 
Table III .—Effect of proximity of healthy hills to hills with the spindling-tuber disease 
1921 
1922 progeny. 
Field. 
Lot. 
Variety. 
Spin¬ 
dling 
tuber in 
field. 
Number of 
healthy hills 
and location. 
Number 
of tuber 
Spin¬ 
dling 
Mosaic. 
Ad¬ 
jacent. 
Not ad¬ 
jacent. 
units. 
tuber. 
A / 
1 
Green Mountain. 
Per cent. 
I 
IO 
47 
40 
42 
38 
47 
5 i 
Per cent . 
30 
0 
Per cent, 
a 6 
Cl 2 
A .{ 
2 
.do. 
I 
IO 
B .{ 
1 
Irish Cobbler. 
I S 
x 5 
5 
5 
Cioo 
IO 
90 
71 
85 
63 
60 
2 
.do. 
IO 
1 
.do. 
IO 
c .{ 
2 
.do. 
IO 
D. 
( b ) 
Bliss Triumph. 
48 
2 9 
° Bulk stock contained io per cent mosaic in 1921 and 17 per cent in 1922. 
6 No spindling tuber in 1920. 
c Adjacent plot. Also 100 per cent mosaic. 
Measurements were made of a number of lots of tubers grown in 1921, 
using a slide caliper of special construction duplicating one devised by 
F. A. Krantz, of the Minnesota Agricultural Experiment Station. The 
longest dimension parallel to the structural axis of the tuber was con¬ 
sidered the length, while the greatest and least dimensions perpendicular 
to the axis were called, respectively, the width and depth. Each lot 
consisted of tubers taken at random from the top of a barrelful that had 
been picked up by chance in the field. When each tuber was measured, 
a record was also made of the presence or absence of spindling-tuber 
symptoms. The results of measuring several Green Mountain lots are 
summarized in Tables IV, V, and VI. The first three lots in each table 
consist of diseased tubers, but they were selected in three successive 
years, respectively. Their similarity in the correlation tables (Table IV) 
and in the ratios calculated for L/W (length/width) and W/D (width/ 
depth) in Table V show how persistent the dimensional characteristics are 
when once the disease has entered the tubers and reduced their width, 
their similarity being more significant for W/D than for L/W. The 
fourth and last lots, from two different strains, are both healthy 
and are much more alike than diseased and healthy parts of the same 
strain or even of the same 1921 plot, especially in W/D. The fifth and 
sixth lots, grown in the same 1921 plot, are similar although grown on 
two types of soil, having about 40 per cent of the tubers diseased, and 
are midway between healthy and diseased lots in dimensional char¬ 
acteristics. It is clear, therefore, that there is a high correlation between 
mechanically determined dimensions and diagnosis of the spindling- 
tuber disease from tuber symptoms, even when this diagnosis was made 
one or two years previously. Mosaic as well as soil had no apparent 
