ADAPTATION. 2J 



of sulphate of iron but without giving any explanation. 

 Sachs attributes the formation of the new chlorophyll cor- 

 puscles to the iron itself. 



According to Max Tord, sulphate of iron placed in solu- 

 tion at the foot of the vine transforms the carbonate of 

 lime dissolved in the water of the soil charged with car- 

 bonic acid into sulphate of lime This explanation is no 

 doubt partly correct, for by spraying chlorotic vines with 

 sulphuric acid one seems to succeed in causing the reappear- 

 ance of the green colour, but it is also very probable that the 

 sulphate of iron has a direct action on the vine after being 

 absorbed by the roots. This is proved by^ its action and that 

 of other salts of iron soluble in the sappy liquids of the 

 vine. In this case, it is true their efficacy may be attributed 

 to their acidity. Chlorotic leaves are less acid than green 

 leaves, as shown by Gouirand in the following table: 



Acidity per 1,000. 

 Chlorotic leaves in calcareous soil . . . . . . 2.63 



Green 4 . 65 



non-calcareous soil . . . . 5.73 



Fremy noticed that the reappearance of the green colour 

 in etiolated plants could be brought about by surrounding 

 them with acid vapours. But Gouirand, by spraying the 

 leaves with the diluted acids of the salts of iron above men- 

 tioned, did not obtain any appreciable results. 



Whatever may be the cause, the beneficial effects of many 

 iron compounds are certain. If it is not yet possible to give 

 a satisfactory explanation of these phenomena, one can, how- 

 ever, in practice, derive advantage from them. Of all the 

 iron salts above-studied the sulphate is, with slight difference, 

 the most efficacious; it must, therefore, be utilized in prefer- 

 ence to any other. 



It may be used in different ways. In fine pulverized 

 crystals, spread on the soil round the stump, it does not give 

 very good results. Is this because it is decomposed there 

 and then by the undissolved carbonate of lime before it has 

 penetrated to the roots? Whatever the cause may be. under 

 this shape it only gives satisfactory results when used in large 

 quantites (2% or 4% Ibs. per vine) and before the winter 

 rains are over; later on its action is nil, except in cases where 

 the application is followed by heavy irrigation. 



It is more effective in solution The quantity used should 



