THE ASH OF PLANTS. 193 
In figure 26, a represents the appearance of a leaf, magnified 414 diam- 
eters. Around the borders are seen the scales of cagbonate of lime; 
some of these have been detached, leaving round pits on the surface of 
the leaf: e, d, exhibit the scales themselves, ¢ in protile: b shows a leaf, 
freed from its incrustation by an acid, aud from its cuticle by potash- 
solution, so as to exhibit the veins, (ducts,) and glands, whose course 
the carbonate of lime chiefly takes in its passage through the plant. 
Further as to the state of ash-ingredients,—It is by no 
means true that the ash-ingredients always exist in plants 
in the forms under which they are otherwise familiar 
to us, 
Arendt and Hellriegel have studied the proportions of 
soluble and insoluble matters, the former in the ripe oat 
plant, and the latter in clover at various stages of growth. 
Arendt extracted from the leaves and stems of the oat- 
plant, after thorough grinding, the whole of the soluble 
matters by repeated washings with water.* He found that 
all the sulphuric acid and all the chlorine were soluble. 
Nearly all the phosphoric acid was removed by water. The 
larger share of the lime, magnesia, soda, and potash, was 
soluble, though a portion of each escaped solution. Oxide 
of iron was found in both the soluble and insoluble state. 
In the leaves, iron was found among the insoluble matters 
after all phosphoric acid had beenremoved. Finally, silica 
was mostly insoluble, though in all cases a small quantity 
occurred in the soluble condition, viz., 3-8 parts in 10,000 
of the dry plant. (Wachsthum der Haferpflanze, pp. 168, 
183-4, See, also, table on p. 198.) 
Weiss and Wiesner have found by microchemical investi- 
gation that iron exists as insoluble compounds of protox- 
ide and sesquioxide, both in the cell-membrane and in the 
cell-contents. (Sitz’berichte der Wiener Akad., 40, 278.) 
Hellriegel found that a larger proportion of the various 
bases was soluble in young clover than in the mature 
plant. As a rule, the leaves gave most soluble matters, 
* To extract the soluble parts of the graén in this way was impassible, 
9 
