408 



SCIENCE 



[N. S. Vol. XXXVIII. No. 977 



for its presence, and the methods for its 

 quantitative estimation. The quantitative es- 

 timation is illustrated in a majority of the 

 cases by an example, so that the student can 

 not go astray. Perhaps in some of these 

 cases the calculations could have been 

 omitted, for many are so simple that any one 

 who could understand the directions should 

 be able to calculate percentage, etc., but it is 

 better to err in being too explicit rather than 

 be too obtuse. 



The literature has been w^ell reviewed, but, 

 unfortunately, the book contains no author in- 

 dex, so that the numerous author citations 

 lose a very considerable part of their value. 

 It is to be hoped that this feature will be 

 remedied in a second edition. 



The book is well printed on good paper, and 

 is remarkably free from typographical errors. 

 It should prove a useful volume to the aver- 

 age chemist, and invaluable to the plant 

 physiologist or the teacher of plant chemistry, 

 both as a reference book and as a text-book. 

 Needless to add it should be in every chemical 

 library. Eoss Aiken Gortner 



SPECIAL ABTICLES 



THE ORGANIZATION OF THE CELL WITH RESPECT 

 TO PERMEABILITY 



In studies on permeability it is assumed 

 that we need consider but one surface, namely, 

 the outer " plasma membrane." It seems de- 

 sirable to emphasize that the problem really 

 involves a variety of surfaces' the permeabil- 

 ity of which may be decidedly different. 



Good illustrations of this may be found in 

 many kinds of plant cells. A very favorable 

 object for investigation is afforded by the 

 marine alga Griffithsia. Within the cell wall 

 is a thin layer of protoplasm which surrounds 

 a large central vacuole. The protoplasm 

 therefore forms a sack which is filled with 

 liquid. It is capable of expanding or con- 

 tracting as water is taken up or withdrawn 

 by osmotic exchange. 



^ The term surface is preferred, since a semi- 

 permeable surface may exist where there is no 

 definite membrane. 



If these cells be placed in hypertonic sea 

 water water is withdrawn from the cells and 

 the protoplasmic sack contracts: on replacing 

 the cells in sea water the sack expands to its 

 original size. If in place of hypertonic sea 

 water we use hypertonic NH^Cl the sack like- 

 wise contracts, but the inner wall of the sack 

 contracts a great deal more than its outer 

 wall. The space between the two surfaces 

 which is normally very small may increase 

 until in places it equals one third of the 

 length of the cell. 



There are, therefore, two surfaces, the outer 

 surface of the protoplasm (" plasma mem- 

 brane ") and the inner surface (vacuole wall) 

 which do not act alike with respect to per- 

 meability. The interpretation of their be- 

 havior may be twofold. In the first place, the 

 outer surface may be regarded as more per- 

 meable to -NHjCl than the inner. The salt 

 would therefore cause the outer surface to 

 contract less than the inner since it is well 

 known that the more freely a substance pene- 

 trates the less is its plasmolyzing power. 



On the other hand, we may have to do with 

 an alteration of permeability produced by the 

 ISTHjCl. If the NHjCl produces an increase 

 of permeability it may cause a contraction 

 by what has been called false plasmolysis.^ 

 If the false plasmolysis of the inner surface 

 is greater than that of the outer the effect 

 which we have witnessed may result. 



It is of course quite possible that both of 

 these interpretations are correct and that we 

 have both true and false plasmolysis con- 

 tributing to the result. The writer is inclined 

 to think that this is the case. 



By lowering the concentration of the NH^Cl 

 we can produce a marked contraction of the 

 inner surface while the outer still retains its 

 full turgidity and shows no sign of contrac- 

 tion. This is most strikingly shown where a 

 living cell adjoins a dead one. The turgidity 

 of the living cell causes its end wall to bulge 

 into the dead cell. As soon as the living cell 

 loses its turgidity the end wall ceases to bulge 

 and becomes nearly flat. It is therefore easy 

 to determine whether the cell is turgid or not. 



="01 Bot. Gazette, 46: 53, 1908; 55: 446, 1913. 



