THE ASH OF PLANTS. 193 



In figure 26, a represents the appearance of a leaf, magnified 4)^ diam 

 eteis. Around the borders are seen the scales of carbonate of lime ; 

 some of these have been detached, leaving round pits on the surface of 

 the leaf: c, d, exhibit the scales themselves, e in profile : b shows a leaf, 

 freed from its incrustation by an acid, and 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 ill both the soluble and insoluble state. 

 In the leaves, iron was found among the insoluble matters 

 after all phosphoric acid had been removed. 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 TIaferpflanze, 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. (Sitdberichte 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 grain in this way wan impossible. 



9 



