46 



which they are absent.^ Results similar to those obtained by Loeb 

 have recently been recorded by other investigators.^ 



That the converse case may also occur is indicated by Loeb's inves- 

 tigations: "Different combinations of ions may exist which all have 

 the same effect. It seems as if the physical condition of the colloids 

 were the essential point and that this might be affected by various 

 ion combinations in the same way." ^ 



It is not to be doubted that many peculiarities in relation to ions 

 will likewise be discovered in i3lants as compared with animals. A 

 case in point is that of magnesium chloride, which in pure solution is 

 eight times as toxic as sodium chloride to roots of the white lupine 

 and of alfalfa while the two salts are about equally toxic when cal- 

 cium is present. Hence lupine roots react toward these two salts in a 

 wholly different manner than do sea-urchin eggs. Furthermore, a 

 comparison of different plants, one with another, or of different organs 

 or stages of development in the same plant, will surely reveal numer- 

 ous dissimilarities. 



The importance of the ion-j^roteid theorj^ as an aid to the study of 

 the effects, both toxic and beneficial, which solutions of electrolytes 

 induce in organisms, can hardly be overestimated. It is to be regarded 

 as the only really scientific explanation of this class of phenomena 

 which has yet been attempted. Incomplete as the theory is in its 

 present form, and many as are the anomalies needing further study, 

 we can not but welcome it as a most promising instrument wherewith 

 to attack the vast problem of the physical properties and energies of 

 protoplasm.'' 



Meanwhile it is highly desirable that the study of ion action upon 

 plants be extended. Experiments should be made with a larger num- 

 ber of different ions, and with mixtures containing more than two 

 kinds of cathions.^ It is most essential that many species of j^lants 

 be tested in order that we may determine what classes of reaction to 

 ions are peculiar to certain groups of organisms and what, if any, may' 



1 Festschrift flir Adolf Fick, p. Ill (1899) . 



-See the papers of Garrey, Anne Moore, Gushing, Lillie, and Stiles cited in the 

 Bibliography, (p. 56). True has lately experimented with Cladophora gracilis 

 grown in various synthetic solutions resembling sea water, and has made the 

 highly interesting discovery that an indefinite prolongation of life could be 

 obtained only when a solution equivalent to sea water in its other components, 

 but containing much more NaCl, was employed. Addition of calcium and potas- 

 sium salts was found necessary in order to neutralize effectively the toxic action 

 of a sodium salt solution, 



^Amer. Journ. Physiology, 3, 443 (1900). 



•^For certain limitations of the theory as now formulated reference should be 

 made to the very important paper of Kahlenberg [Journ. Physical Chem., 5, 339 

 (1901)]. 



^ Loeb's discovery that fertilized eggs of the sea urchin could be developed to the 

 pluteus stage in mixtures of three, but not of two chlorides, indicates that much 

 is to be expected from such an extension of these investigations. See Amer. 

 Journ. Physiology, 3, 441, (1900). 



