TOXIC GASES AS A CONTROL OF THE PEACH-TREE BORER. 17 
the case of the nursery trees, the greatest injury occurred about 
wounds. There was noticeably less injury where the protective tis- 
sue was not ruptured than on the uninjured stems, although in many 
cases the gas had killed large patches and partly girdled uninjured 
* collars. 
FOUR-YEAR ORCHARD TREES. 
Four-year orchard trees showed a still greater resistance to the 
effects of the gas. On September 9, 1916, 28 four-year Champion 
trees were treated in an orchard at Conway, Md., with doses as fol- 
lows : Nine received one-half ounce each, 9 three-fourths of an ounce, 
and 10 one ounce. Five trees of each plat were examined on Novem- 
ber 28, 1916, and the remainder on April 2, 1917. Of the entire 28 
trees, IT showed no injury at all. Of the 9 trees which had received 
the one-half ounce dose 7 showed no injury, while 2 were injured, 1 
moderately and 1 severely. On the three-fourths-ounce plat 5 of 
the 9 trees showed no injury, 4 were injured, 2 severely, 1 moderately, 
and 1 only a trace. On the 1-ounce plat 5 of the 10 trees were un- 
injured; of the remaining 5, 3 showed only a trace of injury, 1 a 
plight injury, and 1 was entirely girdled. Of the entire lot of 28 
trees only 1 was killed outright. While one or two others were 
partly girdled, the one last mentioned was the only tree upon which 
the effects of the fumigation were ever visible above ground. As 
usual the injury occurred more or less irrespective of dosage, its 
severity varying with the condition of the tree with respect to insect 
wounds, etc. While it was apparent that four-year trees could not 
be fumigated without more or less injury on lacerated stems, there was 
a decided diminution in its severity on trees of this age compared to 
those younger. 
The extent to which the epidermal and cork layers of the bark are 
responsible for the protection of the tree was illustrated by an ex- 
periment at Springfield in 1916. A block of eight 10-year-old trees 
was treated with 1, 2, 3, and 4 ounce doses on July 20, two trees re- 
ceiving each dose. On August 26 they were examined and no trace of 
injury found. However, in making the examination the trees of the 2, 
3, and 4 ounce plats were considerably scarified, the outer layer of the 
bark being largely pared and scraped away. These trees were re- 
treated with the same dose August 26, and examined again on Octo- 
ber 28. On the 1-ounce plat where the collars were not scarified no 
injury had developed. On the other plats all the trees were injured 
severely, and in two cases completely girdled. On the other hand, 
trees of the same age in adjoining rows withstood during the same 
period continuous fumigation for 125 days without injury. ^ 
