Maya, 1921 Effect of Ferrous Sulphate on Chlorosis of Conifers 
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 ponderosa), Jeffrey pine {Pintis 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 (17) 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 
secoiid 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. 
