MacDougal: tubers of isopyrum biternatum. 511 



and in the other \ per cent, of the salt. Pour days later in 

 the 1 per cent, solutions only occasional starch bodies were 

 found. In the \ per cent, solution of both substances numerous 

 granules were formed. In both these instances the nucleus 

 seemed extraordinarily large and ragged in outline after treat- 

 ment with potassium-iodide-iodine. Many similar experiments 

 show beyond doubt that in proportions as great as 1 per cent, 

 these salts hinder the condensation of the carbohydrates. The 

 influence upon the translocation and absorption of the sugar so- 

 lution, appeared to be the same in the use of both substances. 

 Since the cells in the beginning of the feeding experiments 

 were almost saturated with sugar, however, it appears that the 

 influence of the stronger solution is such as to inhibit the con- 

 densation of the sugars, most probably by changes brought 

 about in them in the acid content. 



Contents of external tissues. The sap of the epidermal cells 

 of the stems, leaves, the endoderm and certain cell of the cortex 

 contains a bitter tasting substance which on the application of 

 potassium-iodide-iodine forms a globular mass or meshwork of 

 aggregations or precipitations reddish brown in color. Washed 

 with water and mounted in glycerine, the color soon fades to a 

 light reddish or yellowish brown. The guard cells of the 

 stomata of the leaves and stems contain a substance which 

 colors a more darkly reddish brown on the addition of the 

 iodine solution, which after washing and mounting in glycerine 

 fades entirety. The original color of both surface and guard 

 cells may be obtained if the glycerine is replaced by water and 

 iodine added as before. The addition of iodine in 96 per cent, 

 alcohol gives a precipitate in the epidermal cells somewhat 

 brighter in color than is obtained by the use of potas- 

 sium-iodide-iodine, while the guard cells react as before. 

 If such sections are J eft in alcohol over night the color 

 disappears entirely, and the absence of reaction when a fresh 

 solution of iodine is added shows that the substance precip- 

 itated has been dissolved in alcohol. In stems which had lain 

 in alcohol for 5 months no trace of this substance could be 

 found, it having been extracted by the fluid. By the use of 

 iodine in water a dull yellowish precipitate was obtained. The 

 precipitate obtained with potassium-iodide-iodine is insoluble 

 in phosphoric, and hydrochloric acids when added in the form 

 of a drop at the edge of the cover glass. Nitric acid, however, 

 causes the precipitate to take the form of irregular jagged 



