34 



SCIENCE 



[N. S. Vol. XLII. No. 1070 



point, however, was stronger than on the main 

 stem, either above or below the branch. Fur- 

 thermore, it was noticed that in passing out 

 an older lateral branch, the cyanide showed 

 a preference for the upper side of the limb. 

 The question arises, How does the cyanide pass 

 through such a plant? If it passed through 

 the vascular bundles without giving a Prus- 

 sian blue test, the oxidases in that tissue would 

 have been destroyed, but even in the stems in 

 which a positive test could be obtained, in the 

 cellulose tissue an oxidase test could still be 

 obtained in the vascular bundles by both benzi- 

 dine and by alpha napthol, although the re- 

 action was not as strong as in the normal 

 plant. 



If the cyanide does not pass through the sap, 

 one would naturally assume that it must pass 

 up by diffusion. The facts, however, do not 

 point to such a conclusion. Diffusion should 

 be as rapid or almost as rapid down the stem 

 of the plant as up the stem, which was not the 

 case. On reaching the succulent tissue, one 

 would expect diffusion to be more rapid, but 

 the opposite is true. A histological examina- 

 tion of the tissues of the plant shows the older 

 stems, with large intercellular spaces in the 

 cellulose tissue, particularly in the cortical 

 layer. The young succulent side-shoots have 

 small or no intercellular spaces. 



One might conceive of the cyanide passing 

 up through the plant in the form of a gas. 

 Potassium cyanide would very readily be 

 broken up by some of the organic acids in the 

 plant, probably carbonic acid, liberating hydro- 

 cyanic acid which could then move up between 

 the cells of the plant without seriously injur- 

 ing them, except where present in great excess. 

 The cells would absorb some of the hydro- 

 cyanic acid, but if the amount be not too 

 great, the cell would oxidize it by its oxidases. 

 Granting its passage as a gas would explain 

 its passage upward faster than downward. It 

 would also explain why, in going out a lateral 

 branch, it travels on the upper side rather 

 than on the lower side and why, on reaching a 

 succulent tissue, with small or no intercellular 

 spaces, it is stopped in its flow. Such tissue 

 with its greater water content would tend to 



dissolve the hydrocyanic in larger quantities 

 than the cell can withstand, this resulting in 

 the death of the tissue. 



A comparative experiment was performed by 

 introducing into the stem of the plant, by 

 means of a siphon tube, a solution of hydro- 

 cyanic acid in distilled water. The siphon was 

 arranged so that the pressure was just sufficient 

 to hold the liquid against the tissue. The 

 edges of the tube were sealed to the stem by 

 means of paraffin. This geranium, upon ex- 

 amination in twenty-four hours, showed the 

 hydrocyanic strongest in the vascular bundles 

 rather than in the cellulose tissue. Diffusion 

 also took place downward, as a very strong re- 

 action for cyanide was obtained, as far as the 

 base of the plant, eight inches below the 

 wound. Diffusion downward, however, was 

 stronger through the cellulose tissue than in 

 the conducting tissue. There seemed to be no 

 difference at the side branches — no stoppage 

 of the hydrocyanic in its course as was found 

 where a crystal of potassium cyanide had been 

 introduced. The results of this experiment 

 where the passage was by diffusion and by con- 

 duction through the vascular system was quite 

 distinct from where the crystal of potassium 

 cyanide had been introduced. Potassium cy- 

 anide was nest tried on an apple tree during 

 March, when the weather was still cold. At 

 the end of two days, the limb into which the 

 cyanide had been introduced was cut off and 

 tested for cyanide. The test showed the cy- 

 anide only in the woody tissue; in fact, by 

 microscopic examination, it was shown to be 

 only in the lumen of the larger tracheae. The 

 distance traveled, however, was not more than 

 two inches. Not all the KCN had disappeared 

 from the opening, probably due to the small 

 amount of sap in the tree and the cold weather. 

 It was noticed that a discoloration appeared in 

 the tissue through which the cyanide had 

 passed. This discoloration agreed exactly with 

 the area in which a Prussian blue reaction 

 could be obtained. When the sap increased in 

 the trees, further tests were made. It was 

 found, however, that although potassium cy- 

 anide disappeared within two days, April lY- 

 19, the hydrocyanic acid had only traveled 



