300 RECORD OF CURRENT RESEARCHES RELATING TO 



through the capillary intercellular passages, another portion through 

 the closed cell-walls, and chiefly or exclusively through the part 

 that remains unthickened, which close up the pores. The process 

 is therefore complicated, and is greatly aided by transpiration. 



5. The more completely a parenchymatous cell or wood-cell is 

 saturated with water, the more slow is the equalizing of the pressure. 

 These cells behave like cells of clay, which when dry allow water to 

 pass readily, but when saturated with water only with difficulty. 



6. While the wall of a parenchymatous cell or wood-cell becomes 

 more permeable for gases the less water it contains, the reverse is 

 the case with periderm-cells. These contain fluid when yoimg and 

 air when mature. As long as the wall is saturated, molecules of fluid 

 force themselves through it and escape as vapour, and air then enters 

 the cell-wall from without. As the wall of the periderm-cells dries 

 up, a change takes place in its molecular structure, which finally 

 prevents the passage of gases through the cell-walls even when there 

 is a great difference in the pressure. 



7. In the case of the elder, the lenticels in the stem are not closed 

 even in the winter, a fact not in accord with the prevalent theory. 



Internal Processes which cause the Curvatures that accompany 

 Growth in Multicellular Organs.* — H. de Vries has paid some atten- 

 tion to this subject, chiefly in relation to tendrils, and states the following 

 as his general conclusion : — Growth in length or elongation depends 

 on the constant production of substances capable of producing osmose 

 in the cell-sap. External and internal causes bring about curvatures 

 in growing multicellular organs by promoting the production of these 

 osmotic substances. 



Function of Vegetable Acids in the Turgidity of Cells.f — H. de 

 Vries suggests and defends the following statement of the part played 

 by these substances : — 



Vegetable acids are the chief substances in the cells of plants 

 that cause turgidity by means of osmose. They exercise this function 

 partly in the free state, partly as acid or neutral salts. 



The vital activity of protoplasm converts the chemical tension 

 of the nutrient substances and of oxygen into the mechanical tension 

 of the acids ; this only requires the access of water in order to pass 

 over into vital energy. 



Function of Oxalic Acid in the Plant.:!: — A recent series of experi- 

 ments by Van der Ploeg seems to throw considerable light on this 

 subject. The materials employed were leaves of the elm, sweet chest- 

 nut, beech, rhubarb, bean, beet, agave, &c. ; the total amount of lime 

 in the ash was first ascertained, then the proportion of lime-salts 

 soluble in water, and finally the amount of oxalic acid. 



In all the leaves examined, with the excej)tion of the beech, an 

 increase of the amount of lime in the ash, relatively to the other 

 mineral constituents, takes place as the leaves grow older, sometimes as 



* 'Bot. Zeit.,' xxxvii. (1879) p. 830. f Ibid., p. 847. 



X ' Uc oxalsuic kalk in de planten ; Academisch proefsclirift dou B. J. van 

 der Ploeg,' Leidun, 1879; see ' Naturforschcr,' xiii. (1880) p. 17. 



