GENERAL PRACTICE. MANURES. 47 



Hydrochloric acid (with which crude forms of potash are treated to form potassic chloride 

 or muriate of potash) has the property of dissolving silica, and this is beneficial to fruit 

 trees that are liable to gum, as the silica strengthens their structure, enabling it to 

 resist fungoid enemies. 



Nitrate of potash or saltpetre acts similarly to, and in some respects better than, the 

 sulphate and muriate, or chloride, but it is dear, and for stone fruits the consensus of 

 opinion is in favour of the chloride, especially when applied along with phosphate. 



Perhaps the most important consideration in respect of potash is that relating to 

 the colour of fruit. The value of fruit for home use or market depends mainly on its 

 appetising appearance. Where there is good colour there is generally high quality, and 

 colour depends on chlorophyll or the green colouring matter of leaves and fruit. When 

 potash is deficient the leaves are pale and defective in colour, and the fruit is pale ; when 

 potash is plentiful the foliage is dark, because the chlorophyll is dense. Then, under 

 the influence of light and air, peaches glow with crimson, Muscat grapes put on their 

 rich amber, and dark grapes their matchless purple. 



Though potash is an important factor, very small quantities are sufficient to maintain 

 the staying powers of fruit trees. For vine and other fruit borders one pound to the 

 square rod (30 square yards) of the higher grades is a proper dressing to apply annu- 

 ally. Poor, sandy, gravelly, chalky soils and peat require potash more than clays, but 

 some clays, especially those derived from shales of the carboniferous strata, require 

 potash ; then the barren clay becomes notably fruitful. Barrenness, indeed, depends not 

 on texture nor even on geological peculiarities, but on the absence of required fruit foods 

 in the soil, their presence constituting fertility or productiveness. 



Magnesia. Constantly present in fruit, it is difficult to ignore this substance. It is 

 removed from the soil to a large extent by fruits, but experiments show little benefit to 

 accrue from its application. The ash of horse-droppings contains 36 per cent, of phos- 

 phate of magnesia, and it is largely present in house sewage. In kainit it exists to the 

 extent of 1 3 per cent. In cultivated land it is easy to understand why no benefit results 

 from the direct application of magnesia ; but orchards too often have all taken away and 

 nothing returned. Sulphate of magnesia or Epsom salts is the best form in which to 

 apply it, and very sparingly, as it readily dissolves. Half to f cwt. is a proper 

 dressing per acre. 



Iron. In not a few soils this is too plentiful, appearing as red and black oxide. It is 

 present in fruits in variable amounts; gooseberries, strawberries, and plums contain most, 



