1988 



Journal of Applied Microscopy 



Artificial Sap Pressure. 



In order to test the effect of sap (water) pressure upon the opening of buds, 

 the following experiment was devised. 



A stem or twig of the tree to be tested is inserted into a piece of rubber 

 tubing, which with its connections are filled with water. This forms the closed 

 short end of a U tube. The bend of the U contains just enough mercury to 

 cause the water to overflow before the twig is inserted in the rubber tube. After 

 inserting the stem, additional mercury is poured into the long arm of the U 

 until the desired pressure is produced. The pressure 

 of the mercury forces the water into the tissues of the 

 stem with a force equal to the weight of the mercury 

 above the point on the long arm of the U ; the 

 point being the surface of the mercury when balanc- 

 ing the water in the short arm. 



Provision is made for restoring the pressure and 

 replacing the water forced into the stem, or lost 

 through it, by inserting a T connection between the 

 end of the U and the base of the stem. The branch 

 of the T is connected with a stout rubber bulb of 75 

 c. c. to 100 c. c. capacity, and between it and T a 

 stop-cock and an automatic valve are placed. 



As now being used, the pressure is maintained at 

 5(10 grams as constantly as possible. Poor heat regu- 

 lation in the laboratory rooms renders considerable 

 variation unavoidable. Twice a day the pressure is 

 restored, after it has fallen by the movement of water into and through the stem. 

 To restore the pressure, water is forced from the bulb past the automatic value 

 and the stop-cock into the water space in the short arm, until the level of the 

 mercury is restored to the 500 gm. level. This gives a height of mercury, with 

 the tubing used, of '2'1 inches above the •• mark. 



The automatic valve (made by fastening a band of rubber across the end of 

 a piece of glass tubing) prevents the return of any water and holds the pressure 

 while turning the stop-cock. By this apparatus, liquid has been forced from the 

 scales of cherry buds at the tips of stems 'iS inches long, forming globules of 

 apparently resinous matter upon the surface of the buds. As yet no other effect 

 has been observed. A check stem is kept in a glass of distilled water (used 

 in the experiment) by the side of the apparatus. Moisture was observed on all 

 buds up to G inches from tips in 24 hours from setting up experiment on Jan- 

 uary 27th. 



A duplicate of the above was set up on February 2d, using maple in place of 

 cherry. The two U tubes are supported on the same stand, and are filled by 

 the same water bulb. But below the automatic valve, each has its own stop- 

 cock, so that either one may be set independently of the other, or the two set at 

 once and at a common pressure. 



Description of Figure. — A, Supply of distilled water for twigs. B, Water bulb for 

 restoring pressure and water. C, Automatic valve, shown separately at C. I), T-tube supply- 

 ing water to the two stems. E, E', T-tubes and stop-cocks for each stem. F, Pinch-cock to 

 prevent the return of water when B is compressed. G, G', Stems in place (diagraniatic). M, 



Apparatus for Testing Sap 

 Pressure. 



Mercury column. W, Water space. 

 Maryland Agricultural College. 



Frederick H. Blodcktt. 



