SCIENCE 



[Vol. LV. No. 1410. 



plasma membranes. This outermost boundary 

 layer consists of a calcium salt of a weak 

 organic acid known since work of Mangin as 

 pectic acid. .Not only is this structure Ca 

 peetate, but in eases other layers of similar 

 chemical character occur in the thickening 

 materials laid down in the more interior parts 

 of the wall. This Ca peetate has been shown 

 to be a stiff adliesive colloid that is formed 

 when pectic acid meets Ca ions. According to 

 authors from Fremy to Bertrand this acid 

 appears when the neutral mother substance 

 pectin is acted on by the enzyme pectase. 



Now in view of the observations of Mangin, 

 Bertrand, and others, and latterly those of 

 Sampson ^''^ there seems to be considerable free- 

 dom in the shifting of cell wall materials into 

 and out of the pectic acid condition, and when 

 Ca ions are present, with the consequent ap- 

 pearance of calcium peetate layers. These 

 chemical shifts are frequently explicable only 

 by relaying them back to internal irritable 

 causes. They appear then in cases to be self- 

 regulated chemical responses to stimuli, per- 

 haps due in the first instance to external con- 

 ditions, but in their immediate application, to 

 internal causes. Thus Sampson finds in the 

 abscission tissue of coleus leaves following the 

 shock due to inflicted injury a change of more 

 or less of the cellulose of cell wall tissues to 

 pectic acid with a disappearance of calcium 

 ions from the cells of the abscission layers 

 and from their walls. Sampson favors the 

 view that the change of cellulose into pectic 

 acid arising from the irritation that sets in 

 motion the train of abscission phenomena is 

 responsible for the disappearance of Ca. 

 Pectic acid being present greatly in excess of 

 the quantity of Ca ions present can not be 

 converted by these ions into the firm colloid, 

 calcium peetate, but creates a thin, mechan- 

 ically weak colloidal medium which mutually 

 interdiffuses with the Ca ions and in pro- 

 portion as the pectic acid exceeds the Ca 

 dilutes and removes it from its original seat. 



In this connection it should be noted as a 

 general observation that the conversion of 

 cellulose into pectose is a usual feature in 



i«Sampson, Homer C, Bot Gaz., 66: 32-53. 1918. 



aging cell walls (Sampson: 48). The shift 

 from pectose to pectic acid follows easily. 



The change in firmness of fruits and vege- 

 tables seen to follow the action of parasitic or 

 of saprophytic fungi seems to be a related 

 phenomenon. Here some form of Wiesner's 

 theory of the generation of organic acids 

 which take possession of the Ca tied up in 

 health in the Ca peetate layers seems likely 

 to apply. With the removal of the Ca by acids 

 formed directly or indirectly by fungi, the 

 peetate layers become pectic acid or something 

 closely akin. Since these substances lack 

 mechanical strength, a slump of the tissues 

 follows. 



It was my good fortune to be able during 

 the winter of 1919-20 to associate Dr. Sophia 

 H. Eckerson of the University of Chicago 

 with our work on this calcium problem, then 

 being carried on in the U. S. Department of 

 Agriculture and with her permission I beg 

 to refer here to some of her findings. She 

 grew seedlings of wheat, maize and white 

 lupine in series of solutions closely paralleling 

 others that were receiving attention, or had 

 received attention in conductivity experiments. 

 Dr. Eckerson applied the methods of micro- 

 chemistry to the study of seedlings grown in 

 potassium solutions in which Bartlett and the 

 author had found a leaching of ions from the 

 seedlings 'nto the solution. Sb-a observed 

 (1) that ions readily entered the cells of the 

 roots, (2) that within twenty-four hours Ca 

 ions began to diffuse out of the calcium pee- 

 tate middle lamella, (3) K peetate was formed 

 instead of the Ca salt and this substance being 

 relatively soluble in water soon dissolved, 

 (4) at this stage, sugars, amino-acids, and 

 salts, chiefly Mg, diffused rapidly out of the 

 roots. Thus we find Dr. Eekerson's micro- 

 chemical evidence giving us the stages of an 

 event already found to exist by means of oui- 

 grosser conductivity work. It was established 

 beyond doubt that not only was the cell wall 

 modified and in part dissolved by the replace- 

 ment of Ca ions by K ions in the solution, but it 

 was shown that the damage goes far more deep- 

 ly into the cell. Analyses of the leach into dis- 

 tilled water by lupine roots has already demon- 

 strated to us that no less than two thirds of 



