B. F. LUTMAN 
The first two observations on leaves of Ulmus are comparable since the 
leaves were situated under similar conditions; the last two records were 
obtained from leaves from the outside of the crown of the tree in one case 
and from a very sunny position in the last instance. Shade seems to lower 
the osmotic pressure even more than a location at the extreme tip of the 
tree increases it. 
The effect of shade on the osmotic strength of the cell sap was even more 
clearly brought out by a series of observations on the leaves of Syringa 
vulgaris: 
Covered 6 days, 1.263° depression, 15.20 atmospheres 
Exposed 6 days, 1.470° " 17.68 
Covered 12 days, 1.010° " 12.15 
Exposed 12 days, 1.608° " 19-34 
Covered 21 days, .963° " 11.58 
Exposed 21 days, 1.505° " 18.10 
Dixon says, regarding other observations on the sap from the roots as 
compared to that of the leaves: "In Syringa the pressure of the sap of 
exposed leaves was found to vary from 14 to 24 atmospheres, while that of 
the roots lay between 4 and 6 atmospheres. In Eucalyptus the osmotic 
pressure of the leaves ranged between 6.1 and 8.4 atmospheres; that of the 
roots was 5.3 atmospheres." 
The effect of wilting on the leaves of Syringa vulgaris is as follows: 
Control, 1-352° depression, 16.26 atmospheres 
Exposed to light without water supply for 4 hours, 2.002° " 24.07 " 
Exposed to light with water supply for four hours, 1.586° " 19.08 " 
Dixon states as one of his conclusions that: "Other things being equal, 
mature leaves showed a higher osmotic pressure than developing leaves." 
No detailed study could have been made at this time as the observations 
were confined to the months of September and October and the latter part 
of August. 
Dixon and Atkins (6), at a later time, observed the osmotic pressure in 
the leaves of Syringa vulgaris throughout an entire growing season and found 
that the rise was constant after April but that a rapid decline occurred a 
few weeks before the leaves dropped from the stem. 
In his book on "Transpiration and ascent of sap" Dixon (4) in a foot- 
note says: "In almost every case it was found that the older leaves, caeteris 
paribus, had a higher osmotic pressure on the same plant. This was ob- 
served in Syringa vulgaris, Vitis Veitchi, Eucalyptus globulus, Hedera helix, 
and especially in Ilex aguifolium. The leaves of the last named evergreen 
persist through four or five periods of growth, and it is generally found at 
any time that the osmotic pressure of the sap of the leaves of each successive 
growth is lower than that of those which precede it." 
Hanning's observations (9) on the differences between the osmotic 
