TOXIC GASES AS A COXTEOL OF THE PEAOH-TEEE BOEER. 17 



the case of the nursery trees, the greatest injury occurred about 

 T.'ouncls. 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-YEAE ORCHAKD TEEES. 



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, 17 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 

 slight injurj^, and 1 was entirely girdled. Of the entire lot of 28 

 trees only 1 was killed outright. AAHiile 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. AVhile 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 3'ounger. 



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 close. 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. 



