January 6, 1922] 



SCIENCE 



the materials yielded were organic and perhaps 

 in large part non-electrolj^tes. Dr. Eckerson 

 finds that the leach into K solutions are largely 

 organic and non-electrolytic. These solutions 

 must have come in considerable part from the 

 cell contents. The permeability of the cell 

 walls had been greatly modified, also the 

 osmotic properties of the plasma membranes. 



These modifications were seen in the passing 

 of materials from within outward. Dr. Ecker- 

 son tested the permeability in the opposite 

 direction. Corn seedlings after five days in a 

 KNO3 solution were placed in a 1 per cent 

 solution of copper sulphate. In one hour the 

 Cu ions had penetrated all of the root tissue. 

 Similar seedlings after five days in a 

 Ca(N03), solution showed the penetration of 

 Cu ions only after twenty-four hours in a 

 similar copper solution. This seems to make it 

 clear that permeability for ingoing ions is also 

 greatly increased by the changes that we have 

 described. 



Experimental work on Mg solutions showed 

 that Mg pectate replaced Ca pectate in solu- 

 tions of Mg salts- It is known that while Mg 

 pectate is not soluble like K pectate and is 

 less permeable it is slightly more permeable 

 than the firmer Ca pectate- 



Dr. Eckerson found in addition to this that 

 the fatal result repeatedly seen in our other 

 work to come after a longer or shorter time to 

 seedlings grown in Mg solutions of more than 

 minimal concentration did not occur until the 

 Ca of the middle lamella had been wholly 

 replaced by Mg. When this had come to pass 

 the cells died. We could perhaps imagine 

 that sufficient uncaptured Mg ions were then 

 free to penetrate the deeper structures of the 

 cell to bring about the fatal upset. 



The conclusion seems well founded that the 

 integrity of the calcium pectate forming the 

 middle lamella was maintained when a suffi- 

 cient quantity of Ca ions was present in the 

 culture solution and with it the normal reten- 

 tion of its contents by the cell. When accord- 

 ing to the laws of mass action this quantity 

 of Ca ions fell below the equilibrium concen- 

 tration, other kations present replaced the Ca 

 in the colloid compound forming the middle 

 lamella. As a result of a long series of experi- 



ments in various culture solutions, it may be 

 said that no kation other than Ca has been 

 found that can replace it in this relation with- 

 out an injurious or fatal change seen in per- 

 meability relations, or without the appearance 

 sooner or later of other toxic response. Mg 

 comes most nearly to replacing Ca, but fails, 

 partly because of the greater permeability of 

 its pectate, chiefly because of the ultimately 

 toxic action of the Mg ions when they reach 

 the deeper lying structures.- 



In view of what has been said, what are we 

 justified in thinking concerning the phe- 

 nomena that lie deeper than cell walls, what 

 about the living content of the cell? I think 

 we are justified in regarding the cell wall and 

 the plasmal membranes that secrete it, and in 

 closest contact with which it lies, as standing 

 in the closest relation. Cell walls, except in 

 specialized locations, are seldom decisive in 

 determining what ions pass through them. 

 They influence, as we have seen, up to a cer- 

 tain quantity the ions that pass into them, 

 through the chemical changes which take place 

 in the walls themselves and thus far may be 

 regarded as having a certain quasi-deter- 

 mining influence. Beyond that, after chemical 

 demands in the walls have been satisfied, more, 

 deeply lying equilibria are concerned. As an 

 ion-containing structure, the cell wall main- 

 tains ion-equilibria subject to the laws of 

 equilibria in colloids, with the living mem- 

 branes with which it stands in most intimate 

 chemical and biological contact. When ion 

 equilibria in the wall are disturbed, this dis- 

 turbance is transmitted to the equilibria of 

 the protoplast that lays it down, modifies it 

 and remains in closest relation to it. Hence 

 it is not surprising that a drastic change in the 

 very chemical composition of parts of the wall 

 itself if continued should work through and 

 perhaps profoundly aii'ect the equilibria of the 

 protoplasm. 



This close relation of protoplasm and cell 

 wall has already been seen in the eases of wall 

 change initiated from within in response to 

 irritation. When cells are melted apart by 

 self -regulatory processes it seems hardly neces- 

 sary to argue the intimate relation of wall 

 change to protoplasm change. In response to 



