PLANT FOODS 7] 



is an exception in the case of Leguminous plants (see pp. 322-355). 

 It has been found that plants of this order have the peculiarity of 

 developing small nodules on their roots. These nodules are supposed 

 to be the work of bacteria which possess the power of absorbing large 

 quantities of nitrogen from the air, thus bringing it into contact with 

 and fertilising the soil. For this reason it is unnecessary to give 

 Leguminous crops, such as Peas, Beans, Lupins &c., nitrogenous 

 manurfes. Indeed dressing the soil growing such crops with nitro- 

 genous manures is likely to do a good deal of mischief. The plants get 

 as it were surfeited with a food which they are capable of obtaining 

 easily for themselves. They may require potash and phosphatic 

 manures but never or rarely ever nitrogenous ones. And soil poor in 

 nitrogen may be enriched by the cultivation of Leguminous plants, 

 afterwards digging or ploughing them into the soil. 



Uses of Nitrogen. — Nitrogen promotes the growth of plants, giving 

 the leaves a deeper colour and making them larger and more luxuriant. 

 It is chiefly obtained from farmyard manure, and the droppings of 

 various animals — pigs, horses, cows, chickens &c. — but never in a free 

 state. Guano — the excreta of seabirds in South America — nitrate of 

 soda, nitrate of potash and sulphate of ammonia are the principal arti- 

 ficial sources which supply nitrogen. The manures containing it 

 require to be used in very small quantities. 



Nitrate of Soda is a mineral salt found in Chili, Peru, and Bolivia, 

 and has of late years become very popular as a quick-acting manure 

 for all kinds of crops. It resembles dirty common salt in appearance, 

 and like that substance readily dissolves in water. Care should there- 

 fore be taken when storing it to deposit it in a dry place, otherwise it 

 will lose much of its value. 



Care must be exercised in its use for garden crops. If too much is 

 given the leaves of the plants wiU shrivel up as if they had been 

 boiled. About 1 lb. to forty square yards is usually considered to be 

 a safe dressing, and it may be applied vrith advantage to such crops 

 as Potatoes, Cabbages and other Cruciferous crops (p. 1113), Beet, 

 Tomatoes &c. 



Owing to its fleeting character, and the ease with which it is 

 washed out of the soil, it is obvious that nitrate of soda is only of real 

 value to the roots of any crop of plants in an actively grovnng state. 

 It should therefore be used to hasten the growth of young plants, or 

 to bring others more quickly into a state of full growth. 



As a rule it is best used by itself and not in conjunction with other 

 manures, such as superphosphate which decomposes it. If mixed with 

 armyard or other organic manures which have the power of extracting 



