B. F. LUTMAN 
latter pressure is developed from the 12.6 percent of cane sugar of the sap, 
while the 1.28 percent of reducing sugars in the leaves helped to maintain 
the equilibrium to some extent. 
General Discussion 
A resume of the observations made on the osmotic pressure of the potato 
plant at different periods of development seems to show the following con- 
ditions to succeed each other: 
1 . The normal pressure in the seed tubers as they are taken from storage 
is between 7 and 10.3 atmospheres. 
2. The sprouts which come from these tubers, not in the soil, exhibit a 
pressure slightly in excess of that of the tubers themselves. 
3. This pressure for the tubers or seed piece is lowered by the absorption 
of water until it drops to 6.82 (August 7), or 6.41 atmospheres (September 
24). 
4. The juice of the leaves of the young plant records a higher osmotic 
pressure than that of the stalk, and the osmotic pressures of the juices from 
both leaves and stalk are greater than that of the juice from the old seed 
piece. 
5. The osmotic pressure becomes greater in the stalk than in the leaves 
after the flower buds are put out and the tubers begin to grow. 
6. The growing tubers maintain an almost constant pressure from the 
time they are of a sufficient size for the determination of pressure until 
maturity. 
7. The pressure in the stalk is less variable than that in the leaves and 
continues high throughout the active tuber and starch period. 
8. The return of cool, rainy weather starts growth of the foliage again, 
and the osmotic pressure in the leaves again becomes greater than that in 
the stalks. 
9. The osmotic pressure in the old plants is higher than that in the 
young ones. 
10. The pressure diminishes again in the very old plants that have lost 
practically all their foliage and sinks to a very low ebb in the yellow-green 
stalks with no foliage. 
These observations have a distinct bearing on certain conclusions, both 
theoretical and practical. 
I. A superior osmotic pressure seems to be necessary for the formation 
of new growth. The sprouts have a greater osmotic pressure than have the 
tubers from which they arise. The leaves have a higher osmotic pressure 
than the stalks during the early growth period while the foliage is being 
produced, but as soon as they lose that predominance, the growth stops and 
is not resumed until the predominance is again assumed, usually late in 
the growing season, in September. 
