Maya, i93 1 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 (19, 20) and the prompt reaction 

 (fig. 2) following the small amount of the sulphate added by the writers 

 in the i 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 i 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 OF 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 (75), and the nonavail- 

 ability of colloidal iron (7, jj) that the trouble was chiefly due to the lack 

 of dissolved iron in the water of certain calcareous soils. However, in the 

 lime 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 



