THE ASH OF PLAHTS. 193 



the analyses of the seeds of cereals, ferric oxide ranges 

 from an unweighable trace to 2 and even 3%. In root 

 crops it has been found as high as 5%. Kekule found 

 in the ash of gluten from wheat 7.1% of ferric oxide. 

 (Jahresbericht der Chem., 1851, p. 715.) Schulz-Fleeth 

 found 17.5% in the ash of the albumin from the juice of 

 ';he potato tuber. The proportion of ash is, however, so 

 small that in case of potato-albumin the ferric oxide 

 amounts to but 0.12 per cent of the dry substance. (Der 

 Rationelle Ackerbau, p. 82.) 



In the ash of v^ood, and especially in that of bark, ferric 

 oxide often exists to the extent of 5 to 10%. The largest 

 percentages have been found in aquatic plants. In the 

 ash of the duckweed (Lemna trisulca) Liebig found 

 7.4%. Gorup-Besanez found in the ash of the leaves of 

 the Trapa natans 29.6%, and in the ash of the fruit- 

 euvelope 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 Trapa natans, we 

 cannot suppose all the iron to be essential, because the 

 larger share of it exists in the tissues as a brown powdery 

 oxide which may be extracted by acids, and has the ap- 

 pearance of having accumulated there mechanically. 



Doubtless a portion of the iron encountered in anal- 

 yses 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. 



Manganese is Unessential to Agricultural Plants. 

 Manganese is commonly much less abundant than iron, 

 and is often, if not usually, as good as wanting in agri- 

 cultural plants. It generally accompanies iron where 

 the latter occurs in considerable quantity. Thus, in the 

 ash of Trapa, the oxide Mn 3 4 was found to the extent 

 of 7.5-14.7%. Sometimes it is found in much larger 

 quantity than oxide of iron ; e. g., C. Fresenius found 

 13 



