Bouyoucos, Transpiration of Wheat Seedlings as Affected etc. 13 



ratio. Also as the density of the cell sap decreases, the degree 

 er power of its physical ])roperties to diminish evaporation decreases, 

 and therefore, the rapidity with which the water tends to go off 

 rises proportionally. Thus, in either case, the amount of water 

 lost increases directly with the reduction in concentration, and 

 since the density of the cell sap diminishes with the increase in 

 dilution of the outside Solution, the increased transpiration per unit 

 of growth as already noted, is probably the result of the reduced 

 intensity of the physical properties of both factors. 



The assum])tion made under the third factor, was tested ex- 

 perimentally, and from all evidence it appears to be correct. This 

 point was investigated by extracting the cell sap of the plants 

 grown in the different coucentrations of Solution and determining 

 its density. The extraction of the plant juice was performed by 

 placing the green plants in a mortar, crushing them with a pestle 

 tili the sap was pressed out, and washing out the latter with 

 distilled water. The pestling and washing were continued tili the 

 plant juice had been taken out, and only the white fiber was left 

 behind. The later was then put in a piece of cheesecloth and 

 rinsed several times in order to wash out every trace of the cell 

 sap, and then pressed very firmly inside of the cloth to strain out 

 all the Solution. The extract was then filtered through ordinary 

 filter paper, its volume brought up to a definite point, and its 

 density determined. For the latter, two methods were used; 

 1) the freezing point; and 2) the electrical resistance, as determined 

 by the Wheatstone bridge. A good deal of preliniinary work was 

 done with both methods, and it was found that both gave exactly 

 the same results, namely, that the density of the cell sap decreased 

 with the diminution in concentration of the outside Solution. Since 

 the resistance method was the quicker and the simpler of the two, 

 the niajority of the final determinations were done by this method. 

 While the resistance may not be as accurate or give as definite 

 quantitative results as the freezing point, it shows, however, the 

 comparative relation sought for. 



The plants used in this work were wheat. Beans were also 

 used, but only in one case. Both kinds of plants were grown in 

 Solution cultures from about three to six weeks, and one kind also 

 in sand cultures. 



In Order that the density of the cell sap may be comparable 

 among the different densities of Solution, exactly the same weight 

 of green plants grown in the various concentrations, was taken. 



Experiment I. This experiment consisted of growing wheat 

 seedlings for 16 days in two diffeient densities of Solution, namely, 

 4500 and 93.5 P. p. m. At the end of the above period they 

 were harvested and exactly 3.9610 grams of green weight was 

 taken, the cell sap was extracted by the method already described, 

 diluted to 200 cc. with distilled water, and the density determined 

 by both methods. The data obtained are given in the following 

 tables. 



