142 
Journal of Agricultural Research 
Vol. XXIV, No. a 
The data indicate that the beginning of new growth had permitted the 
essential equalizing of sap densities, except with bristlecone pine and 
western white pine. It is difficult to see why the density for bristlecone 
pine ishould have remained high without giving it, apparently, a high 
osmotic pressure. The very thin sap of Siberian larch is accounted for 
by the advancement of its growth, which always begins earlier than 
that of any of the native species. 
■ - j . . 
TaplE density of trees in natural habitats after drying weather, December, 
30, 3i> 
apedes. 
Site where collected. 
Sap density. 
biipber pine. 
Yellow pin^* 
I>6dgepole'pme. 
Dougla^ 
Engeltnann spruce. 
2 southwest slope 
6 northwest slope 
6 northwest slope 
12 ridge. 
9 north slope. 
All, 
2 southwest slope 
2 southwest slope 
6 northwest slope 
4 east slope. 
12 ridge. 
All. 
I south slope. 
8 rid^e. 
All. 
2 southwest slope 
4 east slope. 
12 ridge ... 
9 north slope. 
All. 
3 northeast slope 
5 bottom. 
5 bottom. 
All. 
Per cent. 
28. 67 
29. 86 
26. 42 
27. 08 
28.39 
28. o8±o. 45 
26. 75dbo. 59 
27. 24 
27. 61 
27. 42±0,16 
27-35 
26. 40 
28.10 
24.44 
26. 57 ±0. 56 
24.38 
22. 78 
22.16 
23. ii±o. 51 
® On the itaoming of Feb. 23.1918, corresponding spedmens showed 21.05 pcr cent and 25.12 per cent, 
respectivdy* for these two trees. The spedmen of lower sap density in each case was from a young, vigor¬ 
ous tree; that of higher density from a low limb of an old tree badly infested with mistletoe. 
On the whole, while the determinations of osmotic pressure are not 
complete, it is indicated that they were essentially the same when the sap 
densities were nearly the same. We may, therefore, feel safe in assuming 
that for other conditions relative osmotic pressures will be about pro¬ 
portionate to sap densities, which might not be the case if the solutes of 
different species were materially different in composition and molecular 
weights. A boiling-point test made with accumulated solutes from all 
the species shows that an osmotic pressure of about 19 atmospheres may 
be expected when the sap density is 20 per cent. Freezing-point deter- 
