THE ASH OF PLANTS. 197 
single source of sulphur to plants. The sulphurized oils 
of the onion, mustard, horseradish, turnip, etc., likewise 
require sulphates for their organization. 
Phosphates.—The phosphorized oils (protagon) require 
to their elaboration that phosphates or some source of 
phosphorus be at the disposal of the plant. The physio- 
logical function of the phosphates, so abundant in the ce- 
reals, admits of partial explanation. The soluble albumi- 
noids which are formed in the foliage must pass thence 
‘through the cells and ducts of the stem into growing parts 
of the plant, and into the seed, where they accumulate in 
large quantity. But the albuminoids penetrate membranes 
with great difficulty and slowness when in the pure state.. 
According to Schumacher, (Physik der Pflanze, p. 128,) 
the phosphate of potash considerably increases the diffu- 
sive rate of albumin, and thus facilitates its translocation 
in the plant. 
Alkalies and alkali-earths.—The organic acids, viz. : 
oxalic, malic, tartaric, citric, etc., require alkalies and al- 
kali-earths to form the salts which exist in plants, e. g. bi- 
tartrate of potash in the grape, oxalate of lime in beet- 
leaves, malate of lime in tobacco; and without these bases 
it is, perhaps, in most cases impossible for the acids to be 
formed, though in the orange and lemon, citric acid exists 
in the uncombined or free state, and .in various plants, as 
Sempervivum arboreum, and Cacalia ficoides, acids are 
formed during the night which disappear in the day. The 
leaves of these plants are sour in the morning, tasteless at 
noon, and bitter at night. (Heyne & Link).) 
Silica.—The function of silica might appear to be, in case 
of the grasses, sedges, and equisetums, to give rigidity to 
the slender stems of these plants, and enable them to sustain 
the often heavy weight of the fruit. Two circumstances, 
however, embarrass the unqualified acceptance of this no- 
tion, The first is, that the proportion of silica is not great- 
