504 JOURNAL OF FORESTRY 



(4) Considerable difference in effect was produced by various 

 species of grass. 



Experiments by the author near Oxford were as follows: 

 In the month of March, 1910, 123-year-old ash trees were planted 

 at three-foot intervals and the ground kept bare from grass and weeds. 

 On April 25, 1911, the area was divided into two equal parts and on 

 one of them was sown a mixture of grass and clover. The other was 

 kept clean. The table below shows the average height growth under 

 the two conditions in 1911 and 1912 : 



1911 



With grass 29 



Without grass 38 



Studies were also made on the effect of various kinds of grasses 

 and other plants on the ash when grown in pots. Although the infer- 

 ence from this article is that toxic materials thrown off by the roots 

 of the plant are a possible cause of the unfavorable growth of the 

 trees when grown on grass plots the case has by no means as yet 

 been proved. J. W. T. 



Quarterly Journal of Forestry, July, 1917, pp. 212-18. 



