850 
Journal of Agricultural Research 
Vol. XXVIII, No. 9 
Table I .—Effect on sap density of exposure to room temperature 
Depression of freezing 
point in degrees C. 
Osmotic pressure in 
atmospheres 
Species, aspect, and collection date 
Normal 
treatment 
Left stand¬ 
ing 6 hours 
at room 
temper¬ 
ature 
Normal 
; treatment 
Left stand¬ 
ing 6 hours 
at room 
temper¬ 
ature 
Picea engelmanni 
Northern aspect: 
July 18....... 
1.37 
1.62 
16.5 
19.5 
July 22.. .. 
1.17 
2.01 
14.1 
24.2 
Southern aspect: 
July 18....... 
1.16 
2.38 
14.0 
28.6 
July 22______ 
1.15 
1.74 
13.8 
20.9 
Abies lasiocarpa 
Northern aspect, July 22...... 
0.78 
1.85 
9.4 
22.2 
Southern aspect: 
July 18_______ 
1.36 
1. 57 
16.4 
18.9 
July 22....... 
0.98 
1.66 
11.8 
20.0 
Pinus flexilis 
Southern aspect: 
July 18..... 
1.20 
1.92 
14.4 
23.1 
July 22_________ 
1.14 
1. 95 
13.7 
23.4 
It is obvious that the higher concentration in the sap from the tubes which 
were allowed to stand for 6 hours on the laboratory table was not due to evapora¬ 
tion, since the stoppers had not even been removed after the samples were 
collected. 
The fact that the sap which was expressed from these leaves showed a darker 
color and had a very unusual odor, slightly rancid and somewhat alcoholic, 
strongly suggests that oxidation and enzymic action had already set in and that 
the sap density had thereby been materially changed. These results also suggest 
the grave danger of using any method of extracting the sap which provides for 
soaking the leaves in warm water, as this treatment creates conditions which 
are very conducive to enzymic activity. 
When the leaf tissues were thoroughly frozen the tubes were removed from the 
freezing mixture, washed under a warm water tap to remove salt from the sur¬ 
face and by thawing the tissues quickly to enable a more complete plasmolysis. 
The tubes were carefully wiped on the outside and around the mouth to remove any 
remaining salt which may have adhered. The tissues were then removed from 
the tube and folded in a small square of very heavy muslin which had been pre¬ 
viously boiled in two changes of distilled water and carefully dried. The sap 
was then extracted by thorough and complete pressing in a press specially de¬ 
signed for this purpose. 8 9 Several different types of presses were employed but 
most of them failed to exert the pressure required to extract sap from many of 
the plants growing on the semiarid sites and from the conifers having a muci¬ 
laginous sap. The press which finally proved fully satisfactory consisted of a 
heavily tinned press bowl turned from a 4-inch piece of shaft steel, having a 
convex surface rising from the inside of the bottom. A plunger made of similar 
material hollowed out at the end was, by means of the screw in a heavy pipe vise, 
forced down on the tissue lying between the convex surface of the bowl and the 
concave surface of the plunger. 
The screw was turned down slightly every few minutes to maintain a constant 
oozing of the sap from the tissue. The tissue was frequently rearranged and 
8 The writer is under particular obligation to Dr. J. Arthur Harris for material assistance and cooperation 
in this connection. 
