180 HOW CROPS GROW. 



ash of wood of Pinus sylvestris 18.2 | Mn 3 O 4 , and 3.5 |. 

 Fe 2 O 3 . In ash of the seed of colza, Nitzsch found 16.1| 

 Mn 3 O 4 , and 5.5 Fe 3 O 3 . In case of land plants, these high 

 percentages are accidental, and specimens of rao^t of tho 

 plants just named have been analyzed, which were free 

 from all but traces of oxide of manganese. 



Salm-Horstmar concluded from his experiments that 

 oxide of manganese is indispensable to vegetation. Sachs, 

 Knop, and most other experimenters in water-culture, make 

 no mention of this substance in the mixtures, which in 

 their hands have served for the more or less perfect devel 

 opment of a variety of agricultural plants. Birner & 

 Lucanus have demonstrated that manganese is not needful 

 to the oat-plant, and cannot take the place of iron. ( Vs. 

 St., VIII, p. 43.) 



Is Chlorine indispensable to Crops? What has 

 been written of the occurrence of soda in plants ap 

 pears to apply in most respects equally well to chlo 

 rine. In nature, soda, or rather sodium, is generally 

 associated with chlorine as common salt. It is most prob 

 ably in this form that the two substances usually enter 

 the plant, and in the majority of cases, when one of them 

 is present in large quantity, the other exists in correspond 

 ing quantity. Less commonly, the chloi me of plants is in 

 combination with potassium exclusively. 



Chlorine is doubtless never absent froi i the perfect agri 

 cultural plant, as produced under natural Conditions, though 

 its quantity is liable to great variation, and is often very 

 small so small as to be overlooked, except by the careful 

 analyst. In many analyses of grain, chlorine is not men 

 tioned. Its absence, in many cases, is due, without doubt, 

 to the fact that chlorine is readily dissipated from the ash 

 of substances rich in phosphoric, silicic, or sulphuric acids, 

 on prolonged exposure to a high temperature. In the 

 later analyses, in which the vegetable substance, instead 

 of being at once burned to ashes, at a high red heat, is 



