252 
Journal of Agricultural Research voi. xxvi, No. 6 
Table VI .—Comparison of juices from Dibble's Russet during the summer 
Dibble’s Russet. 
July 2. 
July 12. 
July 27. 
Aug. 6. 
Aug. 8 
Sept. 5. 
Sept. 14. 
Leaves. 
| 0. 614 
0. 782 
0. 832 
. 805 
.838 
O. 883 
.813 
.884 
O. 891 
. 840 
• 843 
0. 803 
0. 856 
Stems. 
.486 
.492 
• 654 
• 393 
.648 
. 481 
Old seed piece. 
New tubers. 
■ 637 
. 626 
• 631 
• 589 
■ 546 
Table VII .—Comparison of juices of Early Rose under various conditions 
Early Rose. 
Planted June 25. 
Garden 
sandy soil, 
Garden 
sandy soil, 
Aug. 8. 
Field 
clay soil, 
Aug. 8. 
Plants of 
July 3, 
Aug. 27. 
July 2. 
July 14. 
July 27. 
Aug. 4. 
Leaves. 
| O- 573 
0. 641 
0. 886 
.768 
.791 
0.832 
.729 
•693 
0.858 
. 721 
•737 
i 0.912 
. 850 
. 728 
O. 901 
Stems. 
•533 
. 520 
. 661 
.676 
Old seed piece. 
• 639 
New tubers. 
• 613 
•507 
. 622 
• 633 
The Dibble’s Russet does not show such a marked falling off in osmotic 
pressure in the foliage juices after the heavy rains of September as 
might be expected, but the juice of the stems, especially according to 
the reading of September 14, did not produce much depression. The 
m&ximum readings were obtained on the juice of the younger leaves on 
August 6 and 8. It will be noticed that the depression from the juice of 
the stems on July 27 and August 6 and 8 almost equaled that of the 
young leaves and exceeded that of the older leaves; on July 2, when the 
plants were younger, the depression from the stem juice was much less 
than that from the juice of the leaves. 
The Early Rose followed in general the same general course of increase 
in the atmospheric pressure of the sap until a maximum was reached 
during late July and early August. Unfortunately, no reading was 
made in late August after the plants had started to decline. The juice 
of the stems of this variety never approximated that of the foliage in 
producing freezing point depressions. The nearly similar depressions 
observed for the juices obtained from the various parts of the plants 
grown on sandy soil and on heavy clay soil are to be noted. The potatoes 
on the sandy soil were somewhat more advanced and the older leaves 
had begun to turn yellow, which will explain the comparatively small 
depression produced by the juice of these leaves on August 4 and 8; the 
old leaves had already begun to decline and the material to be withdrawn 
into the stem. The plants used on August 27 were planted on July 3, 
and are not comparable. On that date, they showed about the same 
atmospheric depressions in the juice from the various parts as the plants 
used on August 8. 
The difference in osmotic pressure in the juices of plants raised under 
shade as compared with those grown in the open is shown in Table VIII. 
