May 2 , X9 Effect of FeYYous Sulphate on ChloYosis of ConifeYS 157 



points each show for three different parts of the nursery wilting coeffi- 

 cients of 11.7, 12.6, and 14.3 per cent, respectively. 1 



The species in which the chlorosis has been noted are western yellow 

 pine (Pinus ponder osa), Jeffrey pine (Pinus jeffreyi), Corsican pine (Pinus 

 laricio corsicana], and Douglas fir (Pseudotsuga taxifolia). Of the two 

 most important species grown here, western yellow pine and Douglas fir, 

 the former is the more susceptible, especially during its first year. During 

 the second year, Douglas fir is also considerably affected. 



The yellowing first becomes evident in the leaves of most recent growth, 

 as reported by Sachs (20) for firs and broad-leaved plants. The entire 

 foliage may be affected. In serious cases, the leaves are short, inclined 

 to curl, and are less turgid than normal leaves (as a consequence of 

 lack of sugars and therefore low osmotic pressure) . The terminal bud 

 either fails to develop or is dwarfed and usually abnormally light in 

 color. The height and diameter of the stem, the length of the roots, 

 and especially the ability to form fibrous lateral roots also appear to 

 suffer in typical cases of chlorosis. The disease may occur in patches, or 

 isolated yellow plants may occur. In severe cases death ensues, the 

 parts first discolored being the first to die. 



The greater part of the injury develops after height growth has mainly 

 ceased for the season. A marked functional disturbance is indicated in 

 the apparent inability of chlorotic plants to harden properly for the 

 winter. Chlorotic first-, second-, and third-year seedlings of both Douglas 

 fir and western yellow pine, though not growing with the vigor of green 

 seedlings, continue growth later in the season and are more susceptible 

 to injury by early fall frosts. This recalls the frost susceptibility of 

 chlorotic redwood shoots reported by Peirce (77) and further suggests a 

 relation between chlorosis and low osmotic pressure due to failure to 

 make sugar, as in wilting. Decreased winter loss as a result of a treat- 

 ment which controlled the chlorosis is shown by the data in Table I. 

 Seedlings chlorotic during their first or second year start growth tardily 

 or not at all the following season. The number of dwarfed chlorotic 

 plants which die during the summer is increasingly great during the 

 second and third years in the seed bed. In transplanting, chlorotic 

 seedlings are discarded. 



1 Determined by the indirect method of Briggs and Shantz in the Laboratory of Biophysical Investiga- 

 tions, Bureau of Plant Industry, United States Department of Agriculture- 



