Chapter IX 



167 — Uptake and Movement 



Standard sucrose solutions of known OP can be injected directly into the 

 petioles with little injury to the leaf and at periodic intervals one or two 

 drops can be withdrawn with a micropipette and analyzed by use of a re- 

 fractometer. When such a technique is used it is found there is a very 

 rapid initial change in concentration of the injected solution because there 

 is a tendency for the DPD of the tissue to approach that of the solution. 

 Subsequent to this initial change there is a diurnal fluctuation in the OP 

 of the injected solution following the normal trend of the DPD of the 

 tissue when the plants are growing in the field on a normal day. Figure 

 45 gives some evidence for such a diurnal fluctuation representing changes 

 in the tissue of from less than 1 atmosphere DPD at night to more than 

 5 atmospheres during the period of greatest water deficit in the day. Cul- 

 ture solution plants also exhibit the same general trends. 



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Fig. 46. — DPD values of solutions in the petioles of a squash plant in the labora- 

 tory. Placing the plant in the sun caused a rapid rise in DPD. Reinjection on the 

 second day indicated a DPD of about 3 atmospheres. 



A graphic reflection of the influence of the environment on the DPD 

 of water in the intact plant is illustrated in the case of a plant growing in 

 culture solution in the moderate atmosphere of the laboratory. Figure 46 

 shows the OP of sugar solutions injected into the petioles. As a result of 

 being placed in the sun for 20 minutes at 2:10 p.m. an immediate jump in 

 the OP of the injected solution was observed which gradually returned to 

 the lower steady state upon return of the plant to the laboratory. In this case 

 leaf 1 was originally injected at 9 :00 a.m. on July 1 with a solution having an 

 OP of 2.4 atmospheres. On the following morning leaf 1 was reinjected 

 with a sugar solution of OP 1.8 and leaf 2 with a solution of OP 11.5. 

 There was a very rapid drop in concentration of the solution in leaf 2 and 

 only a slow increase in solution 1, indicating a DPD of less than 3 atmos- 

 pheres in the tissue. 



Rate of Water Movement Through Plants : — Although our knowl- 

 edge of the movement of water in the xylem dates back, as does much of our 



