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CARNEGIE INSTITUTION OF WASHINGTON. 



chloride, less in sodium, and least in potassium chloride. The results to date 

 are summarized below: 



Relative swelling of stem tips in salt compared to that in water as unity. 



These results indicate that the different tissues comprising the young stems 

 do not react in the same manner to the salt solutions. Thus, with the epi- 

 dermis intact around a portion of the stem, the elongation was greatest in either 

 calcium or sodium chloride solution. After the epidermis was removed from 

 the blackberry stems, they swelled most in potassium chloride. 



There is a rather suggestive parallelism with the absorption rates by 

 artificial cells in similar solutions. Such cells, made from paper extraction 

 thimbles, coated with pectin and agar, hardened in alcohol, and lined with 

 agar, absorb most rapidly from a calcium-chloride solution, least from a 

 potassium solution, thus paralleling the results with walnut. If similar 

 artificial cells are lined with an agar and gelatin mixture, they then absorb 

 most rapidly from a sodium-chloride solution and least from potassium 

 chloride, thus corresponding to the behavior of blackberry stem tips with the 

 epidermis on. On the other hand, artificial cells prepared with an outer 

 coating of agar alone, and lined with gelatin and agar, absorb most rapidly 

 from a potassium-chloride solution and least rapidly from calcium chloride. 

 This latter is, then, similar to the swelling of blackberry stem tips without the 

 epidermis. 



The epidermis on the stem tips of blackberry appears thus to exert an 

 influence on their swelling which is strikingly similar to the effect of a pectin- 

 ized outer layer on the absorbtion of the artificial cells. In the absence of the 

 epidermis, the stem tips of blackberry appear to swell in the different solutions 

 used in a manner parallel to the relative rates of absorption by artificial cells 

 coated with agar alone. It is not assumed from this that the apparent simi- 

 larity in behavior of artificial cells and of the cell-masses in the several tissues 

 of the stem is necessarily caused by similar arrangements of similar cell 

 components in each case. It is quite possible that widely different colloidal 

 substances may react in a like manner to the series of salt solutions here dealt 

 with; further, the mechanism in the swelling of the plant cells involves several 

 considerations which do not enter into the operation of the artificial cells. 

 The swelling of the plant cells requires stretching of the cell walls, and any 

 agency which would render them more elastic might also permit greater 

 swelling, whereas a similar action on the walls of the artificial cell would 

 decrease the excretion from it and thus decrease the amount of apparent 

 absorption. Nevertheless, the similarity of results by the two methods of 



