July 2, 1915] 



SCIENCE 



35 



about a foot and a half through the woody 

 portion of the stem. No Prussian blue re- 

 action could be obtained in the bark or in the 

 cambium layer, at any time. Thinking that 

 it might be possible that the cyanide would 

 pass rapidly through the tracheae and later be 

 destroyed, making a positive cyanide test im- 

 possible, a large apple tree was selected for a 

 further experiment. Near the base a hole 

 three quarters of an inch in diameter was 

 bored into the wood. This was plugged up 

 with potassium cyanide, corked and the edges 

 of the cork sealed with collodion. A number 

 of other holes were bored into the tree, one at 

 a distance of a foot above the cyanide opening 

 and four others at varying distances up the 

 tree. These holes were about a half inch in 

 diameter and one and one haK to two inches 

 in depth. Rubber stoppers through which were 

 passed glass tubes, sealed at the outer end and 

 containing distilled water, were placed in 

 these holes and the edges sealed with collodion. 

 These were quite comparable to the burrows 

 of a wood-boring insect, and as hydrocyanic is 

 very soluble in water, the water in the tube 

 would dissolve any hydrocyanic passing into 

 these holes. With a negative test in these 

 tubes, the hope of destroying wood-borers ex- 

 tensively through the tree would vanish. The 

 tubes were examined from day to day for the 

 presence of cyanide. Although, by the 22d, all 

 the cyanide had disappeared from the open- 

 ing, no test could be obtained in any of the 

 tubes, either by precipitation with silver nitrate 

 or by the Prussian blue reaction. On April 29, 

 the tree was examined to determine the path 

 of the hydrocyanic acid. It was found that 

 the hydrocyanic acid had passed through an 

 area varying from an inch to a half inch in 

 diameter, beginning at the upper side of the 

 hole, next to the cork, and had traveled through 

 the woody tissue, missing the first hole con- 

 taining a tube, by about two inches, continu- 

 ing up the tree to a height of about seven feet, 

 where the test became weaker and finally nega- 

 tive. The highest opening in the tree, which 

 was at a height of about six and one half feet, 

 was missed by less than a half inch, the course 

 of the hydrocyanic having been interrupted by 



a knot which it had gone around or otherwise 

 a positive test might have been obtained in this 

 tube. 



In the other trees, it was noticed that the 

 hydrocyanic passed through a particular area 

 which had its point of departure on the upper 

 side of the cyanide hole, next to the cork. If 

 the hole drilled in the tree is at right angles to 

 the tree, the hydrocyanic passes up evenly from 

 the upper side of the hole but does not diffuse 

 throughout the wood. 



From these experiments, it seems that unless 

 one could collect their wood-borers and have 

 them located definitely in the tree, that treat- 

 ment would be of little or no value. It might 

 be locally applied where the wood-borer is defi- 

 nitely located, by drilling a hole just beneath it 

 and introducing the potassium cyanide or 

 where the borer has made a large burrow one 

 might successfully introduce the potassium 

 cyanide into the burrow. For the larger num- 

 ber of wood-borers, such as inhabit our oaks — 

 boring in the cambium layer — this treatment 

 would have little or no value, as the hydro- 

 cyanic does not travel in the cambium but 

 only through the old trache£e. For sucking 

 insects, which feed at the vascular bundles, it 

 does not seem that the cyanide could be suc- 

 cessfully used. In the light of these experi- 

 ments, it seems that the Spanish broom upon 

 which Professor Sanford destroyed his Aus- 

 tralian bugs, must have a peculiar structure 

 to permit the cyanide to pass through an area 

 reached by the Australian bug. If it is a 

 semi-woody plant, similar to the geranium, it 

 would be conceivable that hydrocyanic acid 

 would pass through the cortical layer and be 

 of some value. To be successful against suck- 

 ing insects, it would have to pass through the 

 vascular system where the insects feed or be- 

 tween the outer surface and the vascular sys- 

 tem. The latter is possible in herbaceous Ofr 

 semi-woody plants but would greatly endanger 

 the life of the plant. 



In woody trees, where its path is in the older 

 trachese, there seems to be no danger to the 

 tree, as these tracheae are already dead. Ex- 

 cessive amounts might prove dangerous. It is 

 conceivable that the amount used by Professor 



