178 HOW CROPS GROW. 



36, p. 391,) and Anderson, (Trans. High, and Ag. 

 1855-7, p. 349,) that the ash of sea-weeds is, in general, 

 as rich, or even richer, in potash than in soda. In 14 

 analyses, by Forchhammer, the average amount of Fodn 

 in the dry weed was 3.1 per cent; that of potash 2.5 per 

 cent. In Anderson s results, the percentage of potash i 

 invariably higher than that of soda.* 



Analogy with land-plants would lead to the inference 

 that tho soda of the sea-weeds is in a great degree acci 

 dental, although, necessarily, special investigations are re 

 quired to establish a point like this, 



Oxide of Iron is essential to plants. It is abundant 

 ly proved that a minute quantity of oxide of iron, Fe Q O 3 , 

 is essential to growth, though the agricultural plant 

 may be perfect if provided with so little as to be 

 discoverable in its ash only by sensitive tests. Accord 

 ing to Salm-Horstmar, the protoxide of iron is indispen 

 sable to the colza plant. ( Versuche, etc., p. 35.) Knop as 

 serts that maize, which refuses to grow in entire absence 

 of oxide of iron, flourishes when the phosphate of iron, 

 which is exceedingly insoluble, is simply suspended in the 

 solution that bathes its roots for the first four weeks only 

 of the growth of the plant. (Vs. St. V,p. 101.) 



We find that the quantity of oxide of iron given in the 

 analyses of the ashes of agricultural plants is small, being 

 usually less than one per cent. 



Here, too, considerable variations are observed. In the 

 analyses of the seeds of cereals, oxide of iron 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 oxide of iron. (Jahres 

 bericht der Chem., 1851, p. 715.) Schulz-Fleeth found 

 17.5 | in the ash of the albumin from the juice of the 



* Doubtless dut to the fact that the material used by Anderson was freed bj 

 washing from adhering common salt. 



