38 TRANSPIRATION IN A DESERT PERENNIAL. 



STUDIES INVOLVING FACTORS CORRELATED WITH TRANS- 

 PIRATION BEHAVIOR. 



DAILY COURSE OF STOMATAL MOVEMENT. 

 METHODS. 



For the investigation of stomatal behavior in Parkinsonia the absolute 

 alcohol method used by Lloyd* was tried and found to be satisfactory in the 

 case of leaves of potted plants and of very young plants growing in the open; 

 but it could not be used on the leaves or twigs of adult trees, since in the case 

 of the leaves much of the mesophyll adhered to the peeled epidermis and 

 in the case of the twigs the epidermis came off without the guard cells, 

 which are sunken in deep pits. An effort was made to find some method by 

 which the leaf as a whole could be used. Picric acid was dried at about 40 

 C., cooled, and put into cedar oil until a saturated solution with picric acid 

 in suspension was made. Whole leaves and parts of leaves were put into 

 this mixture and left there until they were cleared sufficiently to be seen by 

 reflected electric light through a microscope. Picric acid was used because 

 of its known properties as a " fixative." Since an aqueous solution could 

 not be used without causing a disturbance of the water content of the cells, 

 cedar oil was selected as a solvent, on account of its ability to penetrate and 

 " clear " fresh plant tissues. The theory of the action of this mixture on the 

 tissues is pure conjecture, but since it was the theory that suggested the use 

 of the materials it is given here for what it may be worth. The picric acid 

 is carried by the cedar oil into the tissues of the leaf, and as soon as it meets 

 the water in the cell walls it goes into aqueous solution and then acts upon 

 the protoplasmic lining within, making it impermeable to water and thus 

 leaving the form of the guard cells undisturbed. 



The only test for this method is of course the checking of results secured 

 with those obtained by some other method. Since the leaves of potted 

 Parkinsonia plants lend themselves to Lloyd's absolute alcohol method, 

 they were used to test the efficiency of the picric acid method, readings being 

 taken by the two methods simultaneously. An extra check was attempted 

 by the use of the direct light method used also by Lloyd (not yet published), 

 but the leaves did not lend themselves to this method. 



EXPERIMENT FOR TESTING THE PICRIC ACID METHOD. 



Two species of Tradescantia, Cissus laciniata, and a hot-house-grown 

 Parkinsonia microphylla were used for the test. Lloyd's absolute alcohol 

 method worked satisfactorily on all of the plants, but neither the light 

 method nor the picric acid method could be used on either Tradescantia. 

 The picric acid method worked satisfactorily on both the Cissus and the 

 Parkinsonia. The numbers given in the tables represent averages of 20 

 readings each, which were obtained as follows : The entire preparation was 

 examined, the probable average size estimated, and 18 individuals near this 

 size were measured; then one near each extreme was measured and included. 



"Lloyd, F., Physiology of stomata, Cam. Inst. Wash. Pub. 82. 



