PASSAGE OF GASES THROUGH CELLS AND CELL- WALLS 187 



The existence of this ready permeability is shown also by Devaux's 

 researches, in which absorption was induced by exhausting the air of the 

 intercellular spaces, and it is not surprising to find that the result was 

 the same whether the plants were immersed in water or surrounded by 

 saturated air l . 



It is hardly surprising that in many plants special combinations 

 may occur, which may however without difficulty be resolved into their 

 component factors ; the essential principles regulating these have already 

 been given. Thus in the outer wall of the epidermis the layers from 

 without inwards are less and less cuticularized, so that diffusion must go 

 on with increasing readiness in this direction, as a gas passes inwards. The 

 temperature also exercises a certain influence upon gaseous diosmosis, but 

 according to Mangin this is not very marked -. 



Nomenclature. The passage of dissolved gaseous particles through membranes 

 may be termed diosmosis, as such passage is in the case of other dissolved sub- 

 stances. When the gas passes in gaseous form through the pores of the dividing 

 wall (Graham's diffusion and effusion 3 ), it is preferable to speak of filtration when 

 the gas is caused to stream through the pores of the membrane by being under 

 compression on the one side of it, and of gaseous diffusion (interdiffusion) when the 

 movement is the result of the different composition of the air on the two surfaces 

 of the partition wall. When filtration takes place through long narrow canals, as in 

 intercellular spaces, we may speak of capillary streaming (Graham's transpiration). 



Filtration and gaseous diffusion take place through the stomata, lenticels, &c., 

 and their rapidity varies inversely as the square root of the density of the gas con- 

 cerned. The rapidly diosmosing carbon dioxide diffuses more slowly than oxygen or 

 nitrogen, but these differences almost disappear as the influence which the dividing 

 membrane exerts becomes more prominent. We may speak of the diosmosis of 

 gases through membranes, independently of whether mere solution, or chemical 

 combinations, or other agencies, take part in the process. The formula for the 

 passage through a film of paper, as obtained by Exner's researches, is represented by 



C 

 -j=, where C is the coefficient of absorption, and d the density of the gas 4 . 



contains at 5C. about 21.5, at 2OC. about 16-7 c.cm. of gas. Frequently water is not fully saturated, 

 and in the depths of the ocean only two-thirds to one-half, or less, of the possible amount of 

 oxygen may be present. Cf. Bunsen, Gasoinetrische Methoden, 1877; Zacharias, Die Thier- u. 

 Pflanzenwelt d. Susswassers, 1891, p. 15; Devaux, 1. c., p. 53; Goebel, Pflanzenbiol. Stud., 1893, 

 2. Th., p. 248 ; Hu'fner, Archiv f. Anat. u. Physiol., 1897, p. 115 (Physiol. Abth.). 



1 Since in air the exosmosing gas is more rapidly removed, the diosmotic transference might 

 take place somewhat more rapidly in air than in water. Cf. Wiesner, 1889, 1. c. , p. 75- 



2 Mangin, Compt. rend., 1887, T. Civ, p. 1811. Barthelemy Ann. d. sci. nnt., 1868, v. sen, 

 T. ix, p. 287) found that the influence of the temperature was much more pronounced. 



3 Graham, Ann. d. Phys. u. Chemie, 1863, Bd. cxx, p. 418. For the physical relationships 

 the reader is referred to physical textbooks, such as \Vinkelmann, Handb. d. Physik, 1891, Bd. I, 

 p. 640; Reis, Lehrb. d. Physik, 1893, 8. Aufl., p. 235. 



* Cf. Winkelmann, 1. c., p. 651, and the literature there cited. Similar relationships have been 

 found for india-rubber. 



