590 
Journal of Agricultural Research 
Vol. xxm, No. 8 
The plant measurements were taken 35 days, 56 days, and 146 days after 
planting. 
Table II .—Correlation of height (determined at different dates after planting) and yield, 
in Reid Yellow Dent grown from relatively disease-free and diseased seed in infested 
soil, at Bloomington, III., in iqi 8 
Condition of seed. 
Number of 
plants. 
Days after 
planting. 
Average 
height. 
Average 
yield per 
plant. 
Correlation 
coefficient. 
Probable 
error. 
Relative disease-free_ 
157 
35 
Cm. 
91. I 
Gm. 
201. 1 
0 
+0.51a 
0 
±0. 046 
iS7 
56 
187- 3 
201. I 
+ • 5 12 
± .046 
*57 
146 
281. 9 
201. 1 
+ -319 
± .056 
Diseased. 
119 
35 
86.1 
181. 2 
+ -474 
± .042 
119 
56 
189. I 
181. 2 
+ -4SS 
± -043 
119 
146 
275-1 
181. 2 
+ -5 62 
+ -037 
The correlation coefficients in this table range from nearly 6 times to 
nearly 15 times the probable error. Love, of the Plant Breeding Depart¬ 
ment of Cornell University, and others, express the opinion that correlation 
coefficients which are more than 3.8 times the probable error are some¬ 
what significant. King, as quoted by Babcock and Clausen (1), gives the 
following rules for the interpretation of the coefficient of correlation 
according to its relation to the probable error: 
x. If the correlation coefficient is less than the probable error, there is no evidence 
whatever of correlation. 
2. If the correlation coefficient is more than six times the size of the probable error, 
the existence of correlation is a practical certainty. 
3. In cases where the probable error is relatively small: 
(a) If the correlation coefficient is less than 0.3 the correlation can not be con¬ 
sidered at all marked. 
(b) If the correlation coefficient is above 0.5 there is a decided correlation. 
Table III gives correlation coefficients between stalk circumference 
and yield of file same plants studied in Table II and presents the only 
correlations between circumference and yield which appear in this paper. 
They are given at this time in connection with the height data of the 
same plants to show that the two characters are seemingly well correlated. 
Table III .—Correlation of circumference of stalk (measured at different dates after 
planting) and yield in Reid Yellow Dent, grown from relatively disease-free and dis¬ 
eased seed on infested soil, at Bloomington, III., in igi 8 ' 
Condition of seed. 
Number of 
plants. 
Days after 
planting. 
Average cir¬ 
cumference. 
Average 
yield per 
plant. 
Correlation 
coefficient. 
Probable 
error. 
157 
35 
Cm. 
5-6 
Gm. 
201. X 
+0. 618 
±0. 038 
Relatively disease-free.. 
157 
56 
9.4 
201. I 
+ • 47 *& 
db * 088 
157 
146 
9.0 
201. I 
+ -643 
± .036 
”9 
35 
5-3 
181.2 
4 - .643 
± .036 
Diseased. 
119 
56 
9.8 
181. 2 
4 * • 5^8 
± .036 
119 
146 
9.2 
x8x. 2 
+ . 620 
± -033 
