VI] OF THE FORMATION OF MEMBRANES 453 



enormously, the older histological descriptions. We can no longer 

 be content with such statements as that of Strasbiirger, that 

 membrane-formation in general is associated with the "activity of 

 the kinoplasm," or that of Harper that a certain spore-membrane 

 arises directly from the astral rays*. In short, we have easily 

 reached the general conclusion that the formation of a cell-wall or 

 cell-membrane is a chemico-physical phenomenon, which the purely 

 objective methods of the biological microscopist do not suffice to 

 interpret. 



Having reached this conclusion we may wait patiently, and 

 confidently, for more. But when the physico-chemical nature of 

 these phenomena is admitted, and their dependence on adsorption 

 recognised, or at least assumed, we have still to remember that the 

 chemist himself is none too certain of his ground.. He still finds it 

 hardj now and then, to teU how far adsorption and direct chemical 

 action go their way together, what parts they severally play, what 

 shares they take in their. intimate cooperation f. 



If the process of adsorption, on which the formation of a mem- 

 brane depends, be itself dependent on the power of the adsorbed 

 substance to lower the surface-tension, it is obvious that adsorption 

 can only take place when the surface-tension already present is 

 greater than zero. It is for this reason that films or threads of 

 creeping protoplasm shew little tendency, or none, to cover them- 

 selves with an encysting membrane; and that it is only when, in 

 an altered phase, the protoplasm has developed a positive surface- 

 tension, and has accordingly gathered itself up into a more or less 

 spherical body, that the tendency to form a membrane is manifested, 

 and the organism develops its "cyst" or cell- wall. The holes in a 

 Globigerina-shell are there "to let the pseudopodia through." They 

 may also be described as due to unequal distribution of surface- 

 energy, such as to prevent shell-substance from being adsorbed 

 here and there, and at the same time inducing a pseudopodium to 

 emerge. 



* Strasbiirger, Ueber Cytoplasmastrukturen, etc., Jahrb. f, wiss. Bot. xxx, 

 1897; R. A. Harper, Kerntheilung und freie Zellbildung ira Ascus, ibid.; cf. 

 Wilson, The Cell in Development, etc., pp. 53-55. 



t The "adsorption theory" of dyeing is a case in point, where the precise mode, 

 or modes, of action seem still far from settled. 



