XIII.] SPECIFIC FUNCTION OF FERTILISERS 261 



of nitrogenous manure, the leaf system becomes exces- 

 sive, a great number of shoots are formed, and the plant 

 tends to go on growing rather than to turn to the 

 production of flowers and fruit. Large quantities of 

 nitrogen are thus valuable for leafy crops of fodder such 

 as grass, kale, cabbages, etc. At the same time it is 

 always found that the rapid growth promoted by 

 excess of nitrogen is both soft and long-jointed, and is 

 very susceptible to attacks of fungoid disease. Cereal 

 crops grown with an excess of nitrogen are readily laid 

 by wind or rain, and the susceptibility to disease of plants 

 overdosed with nitrogen is often well seen under green- 

 house conditions. If nitrogen promotes the vegetative 

 side of the plant, phosphoric acid, on the other hand, 

 hastens maturity and favours the reproductive side of its 

 development, as, for instance, the production of fruit and 

 seed. It is found by experience that the ripening of 

 crops can be accelerated by a liberal use of phosphatic 

 manures; perennial plants like fruit trees can be 

 similarly induced to fruit rather than to grow. All 

 these actions of phosphoric acid are most apparent on 

 heavy soils and in wet seasons, when the natural con- 

 ditions make for slow maturity. Phosphatic manures 

 never give rise to the immediate burst of growth and 

 the dark colour and look of vigour which follows the 

 application of nitrogen ; their effect is only to be seen at 

 harvest time, and particularly in the proportion the 

 fruit bears to the rest of the produce. In consequence, 

 the use of phosphates is often ignored, while nitro- 

 gen has been too much employed because its effects 

 are so manifest. Potash is particularly concerned in the 

 manufacture of carbohydrates by the plant ; it is there- 

 fore particularly valuable to crops which, like mangolds, 

 contain a good deal of sugar or, like potatoes, a good 

 deal of starch. Being so necessary to the assimilation 



