NOTES AND ABSTEACTS. 265 



graph shows a fine specimen well adapted as a bold ornamental plant 

 of fine habit.— C. T. D. 



Nitpog-en Fixation in Colorado Soils. By W. P. Headden 

 {U.S.A. Exp. Stn., Colorado, Bull. 155; February 1910; 8 plates).— In 

 this State complaints have been common that notwithstanding the 

 raising of the standard of agricultural practice results have not been so 

 good as formerly, and an impetus was given to the scientific investi- 

 gation of the cause by the sudden death of a large portion of an estab- 

 lished orchard in the early summer of 1909 (p. 5). The trouble first 

 showed itself as a scorching of the tips of the leaves, which spread over 

 the whole leaves and killed them and in many cases the whole tree, as 

 many as 200 trees dying in a single orchard during the summer. This 

 occurred in several sections of the State and on all kinds of soils, some 

 of the trees being as much as twenty-seven years old. There was only 

 one thing common in all cases, and that was the brown colour of the 

 surface soil (p. 6). Complaints of " brown spots " on which nothing 

 would grow have been common for many years, and they are often 

 erroneously called " black alkali spots " locally. There is no doubt 

 they are becoming more common, and though at first they were reason- 

 ably called " spots " by comparison with the area of the land, they are 

 now often several acres in extent and may be regarded as an outward and 

 extreme manifestation of a condition of things w^hich is becoming very 

 common. Sometimes the affected areas are shining in appearance as if 

 v/et or oily, though in reality dry; sometimes there is an incrustation 

 of the surface soil, while underneath, to a depth of an inch, or even 

 as much as three inches, the soil is of a mealy character and contains 

 crystals which glisten when the surface is turned over with the foot 

 (p. 18). 



Analysis of the soil of affected areas show them all to possess exces- 

 sive quantities of sodic nitrate — as much as 6.54 per cent, in an air-dried 

 sample from the top inch of an area of some eight or ten acres, andS.Bi^ 

 per cent, in a similar sample from two inches of the surface of a smaller 

 area, while a sample taken to the depth of a foot contained 2.83 per 

 cent, of sodic nitrate, equal to 56 tons to the acre in the first twelve 

 inches (p. 48). 



The question of the source of these vast stores of nitrate is being 

 investigated, but much preliminary work has been done and the author 

 has no doubt that they have been, and are being, obtained from the 

 atmosphere by the nitrogen-fixing bacteria present in the soil. The 

 explanation of the sudden dying of established orchard trees is that the 

 accumulation of nitrates in the surface soil was carried down to the 

 roots by a fall of rain at the time when they were most active (p. 44), 

 trees having been experimentally killed in exactly similar fashion by the 

 application of heavy doses of nitrate of soda. There are several things 

 common to these infected areas (p. 45). They are all so situated that 

 while moisture is not excessive there is an adequate supply of it. The 

 surrounding soils are almost uniformly poor in nitrogenous matter and 



