Oct. 9, 1916 
Immobility of Iron in the Plant 
85 
out, the part that had been brushed was a normal green, while the lower, 
unbrushed part of the leaf was strongly chlorotic and remained so until 
treated with iron. This would hardly have been the case if the iron 
were mobile in the leaf tissue. Of course, if a great excess of iron had 
penetrated the epidermis, it might have been translocated to other parts 
of the leaf. 
The inefficiency of spraying the leaves with iron salts, as a means of 
curing the chlorosis of pineapples or grapevines, is probably partially due 
to the immobility of iron in the leaves. 1 With pineapples this treatment 
completely restored the green color to the leaves treated, but new leaves 
formed after the treatment were chlorotic. 
EVIDENCE FROM ASH ANALYSES 
Ash analyses of old, young, and withered leaves generally support the 
view that iron once conducted to the leaf is immobile, although they by 
no means afford proof. It should be borne in mind, however, in judging 
many of the old ash analyses that the determination of the relatively 
small amounts of iron by precipitation as ferric phosphate is not particu¬ 
larly accurate. Also the accuracy of many results where iron was not the 
chief element sought may well have been- affected by contamination. 
The writers have found the colorimetric potassium-sulphocyanate 
method, either in usual form or as modified by Stokes and Cain (9), more 
accurate than the usual method. 
Czapek in his compilation states that old leaves as a rule contain more 
iron than young ones (1, p. 800). The work of Fliche and Grandeau on 
the composition of leaves of different trees at various stages of growth 
supports this (3, p. 487). Analyses made at the Porto Rico Experiment 
Station of leaves from 1-year-old rough-lemon trees {Citrus limonum) 
show the lower or older leaves to be higher in iron than the young leaves. 
The lower and upper leaves of plants from four different soils were 
sampled. The percentages of iron in the dry substance are given in 
Table I. 
Tabi.£ I .—Percentage of iron in young and in old rough-lemon leaves 
Soil No. 
Age of leaves. 
Iron (ReaOa) in dry 
substance. 
I... 
Young.. 
Per cent. 
0. 017 
. O44 
. 021 
*039 
. 012 
. 025 
. OI4 
. 023 
I... 
Old. 
II. 
Young. 
II. 
Old. 
HI. 
Young. 
Ill. 
Old.... 
IV. 
Young. 
IV.. 
Old. 
1 It is significant that with certain kinds of chlorosis of grapevines, treatment of cut stems with the iron 
salts (method of Rassiguier) has proved more efficacious than spraying the foliage. 
