AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
114 
on satisfactory early sorts such as the Irish Cobbler, spraying should be 
a profitable practice in this region. 
Fig. 1. Effect of Bordeaux mixture on vitality of Irish potato plants. 2 rows on 
right unsprayed. On left, sprayed four times with Bordeaux mixture 4-4-50 alone, also 
the same with arsenate of lead, and with arsenate of lead plus nicotine sulphate. Photo¬ 
graphed at Columbia, Missouri, July 25, 1921. 
During the growing season the past year, the weather alternated, with 
short wet periods interspersed between longer hot, dry spells. The result, 
of course, was a sharp variation in soil moisture in the potato field. It 
occurred to the writer that such soil-moisture fluctuations might be the imme¬ 
diate cause of the second growth on the potato tubers, especially on those 
from the sprayed plots, which continued in vigorous growing condition 
during that portion of the summer when the soil-moisture fluctuations 
were sharpest. Furthermore, since Duggar and Bonns (2) have shown 
that a film of Bordeaux spray on the leaves of the potato plant increases 
the transpiration rate, it may be supposed that the water deficit is greater 
in sprayed plants in the field during dry periods. This notion appears 
all the more probable when the larger expanse of leaf surface possessed 
by the sprayed plants is considered. Presumably, tuber growth ceases 
when lack of moisture makes conditions unfavorable for the development 
