24 AMERICAN VINES. 



iron plays a useful part in the formation of chlorophyll. It 

 was easy to conclude from this that its disappearance from 

 the tissues of the plant was due to a deficiency of iron. The 

 first studies of Chauzit and Foex show, however, that in 

 soils where this affection takes place there is the same 

 amount of iron, and often more than in those where the vines 

 remain green. The following figures prove this: 



1. Soil of the School of Agriculture, Montpellier, where 



vines become yellow 2 . 740 



2. Soil of the School of Agriculture, Montpellier, where 



vines do not become yellow 2 . 445 



3. Soil of the School of Agriculture, Montpellier, where 



vines do not become yellow 2 . 000 



And, again, the chalky soils of the environs of Cognac, which 

 are the most refractory to the culture of American vines, 

 often contain a large amount of iron, while in the same 

 locality soils in which chlorosis does not occur contain less 

 iron. 



It is true that in many of these soils iron does not exist 

 in the same state of oxidation, and therefore of assimila- 

 bility. But it has often been obs rved that in the groies 

 soils of the Charentes, the greves soils of Bourgogne, and in 

 many localities of the south where vines beome yellow, that 

 such soils are strongly red-coloured by sesquioxide of iron, 

 which is easily assimilable in this form. And, again, very 

 siliceous soils, almost entirely white and poor in assimilable 

 iron, never bear yellow vines (sandy soils of the Bartonian 

 and Eocene of the south, and the upper Eocene of the 

 Charentes-Inf erieure) . 



On the other hand, Gautier's studies have shown that iron 

 does not enter into the composition of chlorophyll. Should 

 we conclude from this that iron, whatever be the form in 

 which it exists in the soil, cannot prevent chlorosis, and that 

 its absence is in no way an obstacle to the well-being of the 

 American vines ? 



Chlorois and Iron Salts. However, there is an undeniable 

 fact; this is, the positive efficacy of salts of iron on vines 

 and other plants in bringing about the return of the green 

 colour. 



If iron salts do not enter into the composition of chloro- 

 phyll they certainly induce its formation. Many experiments 

 prove this. Eusebe Gris (1840) and, later on, his son, Arthur 



