CELL SAP IN DESERT PLANTS 211 



A solution twice as strong, 0.5 N KNOs effected plasmolysis 

 of all of the epidermal cells within ten minutes. This result 

 accords very well with those of Livingston- who found plasmo- 

 lysis of the epidermal cells of several cacti to take place in a 0.12 

 to 0.5 N KNO3 solution. 



Fouquieria splendens 



The Fouquieria in the glass house was in full leaf. This species 

 has the habit of forming leaves as a direct response to an improve- 

 ment of the water relations. The leaves are retained as long as 

 the water is sufficient in amount, but they wither and fall away 

 with the return of drought. For this reason it is not feasible, as 

 was done with Peganum, to attempt to increase the density of 

 the cell sap directly through a limitation of the water supply. 



In the test of the density of the cell sap the epidermis was 

 stripped from the leaves and was plunged immediately into KNO3 

 solutions of different strengths. Plasmolysis of the epidermal 

 cells was seen to take place slowly in a 0.5 N KNO3 solution, 

 and after having been in the solution ten minutes all epidermal 

 cells w^ere plasmolyzed. The epidermal cells of young roots of 

 the same plants, in a solution of the same density, plasmolyzed 

 very quickly. It was concluded from the response of the cells of 

 the roots that plasmolysis might have occurred in a less dense 

 medium. The limitation of the material on hand at the time 

 of the tests, however, did not permit further study of this point. 



Peganum harmala 



The specimens of Peganum employed in the tests were growing 

 in glass tubes. The shoots were about 2 cm, long and bore rela- 

 tively small leaves. The roots penetrated about 35 cm. 



Portions of the leaves, mainly stripped epidermis, were placed 

 in a normal solution of KNO3 and after a short time, about ten 

 minutes, showed plasmolysis of the epidermal cells — which had 

 taken place very slowly. Tested in less dense KNO3 solutions, 



* The relation of desert plants to soil moisture and to evaporation. Car- 

 negie Institution of Washington. Publication No. 50. 1906. 





TTii 



