May 2,1921 Effect of Ferrous Sulphate on Chlorosis of Conifers 163 
The contrast between the treated and untreated plots of western yellow 
pine at the close of the experiments was very strong throughout. 
No attempt was made to exclude the ferrous sulphate from the roots. 
In view of the high absorptive capacity for iron sulphate of the cal¬ 
careous soil with which Sachs worked (rp, 20 ) and the prompt reaction 
(fig. 2) following the small amount of the sulphate added by the writers 
in the 1 per cent solution treatments on the younger western yellow pine 
seedlings (fig. 2 and Table I), it is believed that the effect of the iron- 
sulphate spraying was due to the entrance of traces of iron into the leaves, 
presumably mostly through the stomata, though Molisch (14) reports it 
as entering through the cuticle. 
Forest officers report that 1 per cent ferrous sulphate sprayings begun 
in April at the Morton Nursery corrected chlorosis in 2-year-old seedlings 
of both jack pine (Pinus banksiana) and western yellow pine by June. 
Scotch pine did not show chlorosis; jack pine showed it most. The con¬ 
trol of the yellowing was not absolute but was practically complete by 
the end of July. The iron-sulphate spray treatment is considered so 
successful that it has now been put into general use on all the jack pine 
and western yellow pine seed beds at the Morton Nursery. 
VALUE OE THE EXPERIMENTS 
It appears from the literature cited in the introduction that on soils 
containing considerable calcium carbonate there often occurs a chlorosis 
which can be corrected by the addition of iron in soluble form to either 
the roots or the leaves. The trouble-making capacity of the calcium 
carbonate, though not always in evidence, appears to be more or less 
specific. Other calcium salts and other carbonates do not seem equally 
effective as causes of chlorosis. It is reasonable to suppose, in view, 
among other things, of the precipitation of iron in alkaline solutions, the 
apparent substitution of iron for calcium in soil (15), and the nonavail¬ 
ability of colloidal iron (7, 11) that the trouble was chiefly due to the lack 
of dissolved iron in the water of certain calcareous soils. However, in the 
lim p soil it might conceivably be that the balance of the solution for plants 
which are not distinctly calciphile is so disturbed as to make more than 
the usual amount of iron necessary to maintain the plants in normal 
health on such soils. A further complication is the fact that the distribu¬ 
tion of chlorosis in different parts of the same plant is sometimes such as to 
indicate that at least part of the difficulty may be due to derangements 
in conduction instead of or in addition to absorption failures. Further¬ 
more, physiologists are not all ready to agree that the lack of green is 
really a symptom of a specific iron hunger, even in cases in which the 
remedial value of iron addition is demonstrated. The writers’ results 
have made no addition to the knowledge of the immediate cause of the 
chlorosis or the way in which the addition of iron works in correcting it. 
These complications are mentioned merely to show that fundamental 
