PLANT PHYSIOLOGY 555 



a plant of A triplex confertifolia being the highest so far recorded 

 for any flowering plant. 



Considerable attention has been devoted to the possible 

 relation between osmotic pressure of cells and their position in 

 the plant, this question being especially of importance in 

 regard to the ascent of water in plants. While earlier observa- 

 tions had been rather inconclusive, Harris, Gortner, and 

 Lawrence (" The Relation between the Osmotic Concentration 

 of Leaf Sap and Height of Leaf Insertion in Trees," Bull. 

 Torrey Bot. Club, 44, 267-286, 191 7) found, in a series of measure- 

 ments made on material of twelve species of trees, that almost 

 without exception the osmotic pressure of the sap extracted 

 from leaf cells is greater the higher the level of insertion of the 

 leaf. No such relation between height of leaf insertion and 

 osmotic pressure of the leaf cells was found by Ursprung and 

 Blum (" tJber die Verteilung des osmotischen Wertes in der 

 Pflanze," Ber. deut. hot. Ges., 34, 88-104, 191 6). In the species 

 examined by these latter authors, namely, Helleborus fcetidus, 

 Urtica dioica, Sedum acre, Fagus sylvatica, and Funaria hygro- 

 metrica, it was found that although cells of the same layer at the 

 same height from the ground have approximately the same 

 osmotic pressure if they are not too far apart, yet neighbouring 

 cells may differ considerably in their osmotic pressure if they are 

 constituents of different layers. The osmotic pressure of the 

 leaf cells appears to increase with age of the leaf. No particular 

 tissue in the leaf appears to be characterised by the possession 

 of the highest osmotic pressure. 



There appears to be a certain amount of correlation between 

 habit and osmotic pressure. Thus Harris, Lawrence, and 

 Gortner (" The Cryoscopic Constants of Expressed Vegetable 

 Saps as related to Local Environmental Conditions in the 

 Arizona Deserts," Physiol. Res., 2, 1-49, 191 6) had found con- 

 siderable variation in the osmotic pressure of the sap expressed 

 from plants growing in the deserts of Arizona, the different 

 groups, in increasing order of osmotic pressure, being (i) winter 

 annuals, (2) perennial shrubs, (3) dwarf shrubs and half shrubs, 

 and (4) shrubs and trees. In a similar investigation on the 

 plants of the Blue Mountains of Jamaica, Harris and Lawrence 

 (" The Osmotic Concentration of the Tissue Fluids of Jamaican 

 Rain-forest Vegetation," Amer. Journ. Bot., 4, 268-298, 191 7) 

 found that the osmotic concentration of the sap expressed 

 from the leaves of woody plants was greater than that from the 

 leaves of herbaceous plants, while this same result has been found 

 by Harris, Gortner, and Lawrence (" On the Differentiation of 

 the Leaf-tissue Fluids of Ligneous and Herbaceous Plants with 

 Respect to Osmotic Concentration and Electrical Conductivity," 

 Journ. Gen. Physiol., 3, 343-345, 192 1 ; " The Osmotic Con- 



