VII 



OF PLATEAU'S BOURRELET 



471 



(7) The bourrelet, a fluid mass connected with a fluid film, is no 

 mere passive phenomenon but has its active influence or dynamical 

 effect. This was pointed out by Willard Gibbs*, and Plateau's 

 bourrelet is more often called, nowadays, "Gibbs's Ring." The ring 

 is continuous in phase with the interior of the film, and fluid is 

 sucked into it from the latter, which thins rapidly; and this, 

 becoming a more potent factor of unrest than gravity itself, leads 

 presently to the rupture of the film. Plateau's explanation of his 

 bourrelet as a ''surface of continuity" is thus but a part, and a 

 small part of the story. 



(8) In the succulent, or parenchymatous, tissue of a vegetable, 

 the cells have their internal corners rounded off (Fig. 156) in a way 

 which might suggest the bourrelet, but comes pf another cause. 



Fig. 156. Parenchyma of maize ; shewing intercellular spaces. 



Where the angles are rounded off the cell-walls tend to split apart 

 from one another, and each cell seems tending to withdraw, as far 

 as it can, into a sphere; and this happens, not when the tissue is 

 young and the cell-walls tender and quasi-fluid, but later on, when 

 cellulose is forming freely at the surface of the cell. The cell- walls 

 no longer meet as fluid films, but are stiffening into pelHcles; the 

 cells, which began as an association of bubbles, are now so many 

 balls, in solid contact or partial detachment; and flexibility and 

 elasticity have taken the place of the capillary forces of an earlier 

 and more liquid phase f. 



* Collected Works, i, p. 309. 

 t J. H. Priestley, Cell-growth , 

 pp. 54-81, 1929. 



, in the flowering plant, New Phytologist, xxviii, 



