24 The Profitable Culture of Vegetables. 



are some cases, as for instance with spring cabbage or lettuce, 

 where an extra vigorous vegetative growth is to be desired, 

 but in many other cases a too-abundant supply of nitrogen 

 would be harmful. Other plant foods such as phosphoric acid 

 and potash, &c., in whatever excess they may be present in the 

 soil, are only taken up by the plant in proportion to its growth, 

 which is dependent upon the nitrogen supply, but with an 

 excess of available nitrogen the growth is luxuriant and sappy, 

 and susceptible to the attacks of fungoid diseases ; maturity is 

 deferred and the crop is badly ripened. Therefore, when the 

 growth of the plant appears to be healthy and sufficiently 

 vigorous applications of nitrogen should not be given unless 

 accompanied by other ingredients to make a well-balanced 

 plant food. 



PHOSPHORIC ACID appears to have the function of causing 

 fruitfulness. Its action promotes the formation of flowers and 

 seeds. Whilst an excesss of nitrogen delays maturity the 

 opposite is the effect of phosphoric acid as it hastens the pro- 

 cess of ripening; consequently, when plants are growing too 

 gross and sappy an application of a readily-available phosphatic 

 manure will do much to correct this tendency and restore the 

 balance. Phosphates also have a beneficial effect in en- 

 couraging root-growth in young plants. 



POTASH plays a very important part in the structure of plants. 

 Whilst nitrogen promotes the growth of leaves, with that 

 element alone they would lack substance, but potash adds 

 strength. It assists in forming the fibre of the plant, making 

 sound, fruit-bearing wood, strong tough straw, &c. Potash 

 also forms the base of fruit acids and flavours, and is particu- 

 larly active in the formation of starch and sugar. Whilst 

 phosphoric acid is active in the formation of seed, potash 

 appears to be responsible for the pulp of the fruit, and for the 

 starch and sugar contained in potatoes, beet, &c. It also makes 

 the plant more resistant to the attacks of fungoid diseases, 

 and has a marked effect in promoting the growth of clover, 

 peas, beans, and all leguminous plants. 



Clay soils are usually rich in potash in a state of combination ; 

 by cultivation sufficient of this becomes soluble to supply the 

 needs of most crops, but there are some, such as potatoes, 



