254 
Journal of Agricultural^Research 
Vol. XXVI, No. 6 
All the juices of the tubers produced during the year 1920 seem to 
show a much higher osmotic pressure than those of 1918. No cause for 
this difference is apparent. It is consistent throughout the season, 
however, and so must be due to the particular weather conditions of 
that summer. 
SUMMER OF 1922 
The year 1922 was marked by the wettest June on record, so that it is 
interesting to see the effect such a period would have on the juice of the 
plants. On July 12 the juice of the old leaves had the greatest depres¬ 
sion, an observation that had not been made before. The leaves at this 
date were all of one size, but, as the plants were in bud, the formation of 
new leaves and branches had ceased, and whatever growth was going 
on was in the form of an increase in the size of the older leaves. It is 
probable that all material was actually being removed from the tip 
(smaller) leaves as it was synthesized, and was utilized in other parts of 
the plant. On July 26, two weeks later, however, the juice of the stems 
of the Irish Cobbler and Green Mountain varieties had a very much 
greater depression, but the Dibble’s Russet still showed more in^the old 
leaves. The old leaves were of almost the same sizes as the tip leaves 
in their variety. 
The plants grown under a shade showed on July 17 a lower osmotic 
pressure in all parts except the tubers than did those grown outside and 
watered regularly, so that the ground was almost moist. On September 
1, however, there was not very much difference between the plants 
grown in the open and those in the shade. 
The observations made on August 9 are of interest on account of the 
coolness of the preceding night, when the temperature sank below 40° F. 
The highest pressure seemed to be in the stems, especially in the Green 
Mountain variety. Not much change can be seen in the readings for 
August 15, although the weather then was hot and sultry. 
GENERAL RESULTS FOR 4 YEARS 
A considerable diversity has been shown in the character of the seasons, 
especially with regard to the amount of rainfall during the 4 years in 
which these cryoscopic readings have been made on the potato plants. 
The wet years were 1918 and 1922, while 1919 and 1920 were inclined to 
be dry, especially the early part of the growing season of 1919. Tables 
IX and X show all the data obtained from various varieties of potatoes. 
Tabi,E IX. —Comparison oj juices from Green Mountain plants during four years 
Portion of potato used. 
July 20, 
1918. 
July ai, 
1919. 
July 27, 
1920. 
July 26, 
1922. 
Young leaves. 
8. 07 
7. 84 
8. 07 
6. 10 
8.34 
7.78 
9. 21 
6. 66 
10 . 02 
9.69 
IO. 09 
7.67 
4. 9 1 
9.49 
10. 20 
5. 60 
Old leaves. 
Stems. 
New tubers. 
Portion of potato used. 
Sept, it 
1918. 
Aug. 31, 
1919. 
Sept, s, 
1920. 
Aug. 15, 
1922. 
Young leaves. 
9. 80 
8. 07 
8. 15 
6.88 
7 - 99 
9 - 5 ° 
9 - 5 ° 
S- 84 
Old leaves. 
9 - 75 
8. 98 
6. 16 
9.67 
7.81 
7. IO 
Stems. 
New tubers. 
