SURPLUSES AND DEFICIENCIES 203 



to the plant. The result is arrested development or, in extreme cases, 

 the appearance of pathological conditions. An excess of nitrogen 

 also leads to disturbed nutritive relations and to pathological symptoms. 

 Considerable attention has already been devoted to the question of iron 

 deficiencies and to methods of dealing with them. 



6. Elaborated organic compounds of many kinds have uses in growth 

 processes equal in importance to those of the mineral constituents. 

 Though for the most part they are synthesized within the plant, the 

 materials for their manufacture are water, carbon dioxide and the 

 nutrients just mentioned. 



It is therefore evident that the question of fertilizers for deciduous 

 fruits, in so far as such fertilizers serve more or less directly as nutrients 

 for the plant, centers largely around the proper use of nitrogen. This is 

 far from stating that fertilizers other than those carrying nitrogen are 

 never of direct nutrient value. For instance, work with grapes and 

 strawberries^^ suggests strongly that sulfur-carrying fertilizers in the one 

 case and phosphorus-carrying compounds in the other supplied the plants 

 directly with these nutrients, though it is possible that certain of their 

 indirect influences may have been more important than their direct 

 effects. Furthermore, there is reason to believe that many of the results 

 obtained from the use of phosphorus-, potassium- and calcium-carrying 

 fertilizers on deciduous fruits of different kinds and generally attributed 

 to their direct nutrient value have in reality been due to their functioning 

 in other ways. These statements are not made to minimize the possible 

 effects or uses of fertilizing elements other than nitrogen. That they 

 often are of value in the orchard there is no doubt. The point is that 

 nitrogenous fertilizers act more or less directly as nutrient-carrying 

 substances; others act rather indirectly through correction of unfavorable 

 soil conditions or by protecting the orchard plants from harmful sub- 

 stances or only indirectly as nutrients through assisting the growth of 

 intercrops or cover crops. Clear differentiation between these different 

 modes of operation is important, for only when there is a clear conception 

 of how a fertilizer works can it be used intelligently and with certainty 

 as to results. 



