LABORATORY FOR PLANT PHYSIOLOGY. 47 



inquiries in this laboratory, and the information thus made available has had 

 no little value in the present connection. 



Estimation of the concentration and ionization of immersion liquids and 

 of the cell-sap of sections has been made by the conductivity method. The 

 use of the artificial cell made it possible to determine the osmotic action of the 

 contents, the amount of exosmose of the organic contents, and by conductivity 

 tests the amount of the electrolytes lost from the immersion liquids to be 

 absorbed or combined with the material of the external layers or diffused into 

 the cell contents. 



The widely divergent suites of data that may be secured by the hydration 

 of material from different plants suggest varying composition of the cell. It 

 was therefore arranged that artificial cells should be constructed which should 

 show the action of different colloids in the external layers. Relative 

 permeability is taken to be denoted by the outflow from cells immersed in 

 various solutions. Such data are also supported by determinations of the 

 resistance or conductivity of the immersion liquids or of the cell contents to 

 ascertain the behavior of the electrolytes which may have passed into the cell, 

 been absorbed by the colloids, or combined with some of the material of the 

 external layer. Estimations were also made of the exosmosis of the organic 

 material from the cell contents. 



The design of this cell was described in the annual report of this Depart- 

 ment for 1922. 



Effect of Salt Solutions on Hydration and Swelling of Plant Tissues, by 



F. T. McLean. 



The study of the swelling of plant tissues in salt solutions, previously 

 reported, was continued. This year's results indicate that the difference in 

 the behavior of stem tips of walnut (Juglans major) and of blackberry (Ruhus 

 vitif alius), noted last year, was due to the manner of preparation of the material 

 for testing. The walnut stem tips were sufficiently large so that each tip 

 could be bisected lengthwise. The halves, with the epidermis on, were placed 

 upright in the glass dishes, and their lengthwise swelling in different test 

 solutions was recorded by auxographs. Thus one half of each tip was used 

 for a test in salt and the other was swelled in distilled water for a control. 

 With this treatment, the swelling was greatest in calcium chloride, less in 

 magnesium, and least in sodium and potassium chlorides. The blackberry 

 tips were so small that each one was used entire, and, in order to secure good 

 penetration of the solutions into the tissues, each tip was scraped free of 

 pubescence, one side was sliced off a little, the sections were placed in the 

 dishes and subsequently treated as with walnut. By this treatment most or 

 all of the epidermis was removed from the blackberry sections. When so 

 treated, swelling was greatest in potassium chloride, less in sodium and 

 calcium chlorides. 



Experiments with blackberry were repeated in a similar manner this season, 

 with indeterminate results, but generally agreeing with the previous ones 

 (but no initial shrinkage was noted in any of the solutions). Sections of black- 

 berry were also prepared as nearly as possible in the same manner as the 

 previous walnut sections, i. e., the epidermis was left on them and one side 

 of each was shced off rather deeply; with the epidermis thus in place, the 

 swelling of the blackberry sections in the different solutions gave results more 

 nearly like those for walnut. The swelling was then greatest in calcium 



