THE ASH .OF PLANTS. 179 
potato tuber. The proportion of ash is, however, so small 
that in case of potato-albumin, the oxide of iron amounts 
to but 0.12 per cent of the dry substance. (Der Rationelle 
Ackerbau, p. 82.) 
In the wood, and especially in the bark of trees, oxide 
of iron often exists to the extent of 5-10°|,, The largest 
percentages have been found in aquatic plants. Inthe ash 
of the duck-meat, (Lemna trisulca,) Liebig found 7.4°|,. 
Gorup-Besanez found in the ash of the leaves of the Zrapa 
natans 29.6°|,, and in the ash of the fruit-envelope of the 
same plant 68.6°|,. (Ann. Ch. Ph., 118. p. 223.) 
Probably much of the iron of agricultural and land 
plants is accidental. In case of the Z’rapa natans, we 
cannot suppose all the oxide of iron to ‘be essential, be- 
cause the larger share of it exists in the tissues as a brown 
powder, which may be extracted by acids, and has the ap- 
pearance of having accumulated there mechanically. 
Doubtless a portion of the oxide ‘of iron encountered in 
analyses of agricultural vegetation has ‘never once existed 
within the vegetable tissues, but comes from the soil which 
adheres with great tenacity to all parts of plants. ° 
Oxide of Manganese, Mn, 0,, is unessential to Agri- 
cultural Plants.—This oxide is commonly less abundant 
than oxide of iron, and is often, if not usually, as good as 
wanting in agricultural plants. It generally accompanies 
oxide of iron where the latter occurs in considerable quan- 
tity. Thus, in the ash of Zrapa, it was found to the extent 
of 7.5-14.7°|,. Sometimes it is found in much larger quan- 
tity than oxide of iron; e. g., C. Fresenius found 11.2°|,. 
of oxide of manganese in ash of leaves of the red beech, 
(Fagus sylwatiea,) that contained but 1°|, of oxide of iron. 
Jn the ash of oak leaves, (Quercus robur,) Neubauer found, 
of the former 6.6, of the latter but 1.2°|,. 
In ash of the wood of the larch, (Larix Huropea,) 
Béttinger found 13.5°|, Mn, O, and 4.2°|, Fe, O,, and in 
