Nitrification 



( 115 ) 



Nolana 



utilised by the roots. With the exception of the 

 roots of Leguminous plants, and certain forest trees, 

 which, when growing in soils, containing a. large 

 percentage of humus, have the assistance of 

 saprophiticfumri, collectively known as microrhiza, 

 no plants are ^ole to use ordinary nitrogen. A 

 group of bacteria is able to break up the nitrogen- 

 ous compounds into nitrates, this process being 

 termed nitrification. Certain conditions are neces- 

 sary to enable the bacteria to carry on their work ; 

 these are (a) moisture, (*) heat, (c) oxygen and 

 the presence of lime and some form of phosphorus, 

 e.g., phosphate of lime. Nitrates are always found 

 more abundantly in soils after warm weather, as 



NIVENIA (syn. PAHANOMUS). 



A genus of large, erect - growing, evergreen 

 plants (ord. Proteacese), thriving in the green- 

 house. Propagated by seeds and grown in . a 

 mixture of two parts peat and one part loam, with 

 sand, and good drainage. 



Principal Species : 

 crithrnifolia, 4', Je., grh., 



pur. (mjtt. Protea Lago- 



pus). 



NOCC^EA. 



Small, dwarf-growing, creeping or procumbent, 

 hardy herbaceous plants (ord. Cruciferte), suitable 



media, 2J', Je., grh., pur. 

 (syn. Protea spicata). 



Photo: Cassell it Company, Ltd. 



NlCOTIANA TOMENTOSA (see p. 114). 



heat is essential for the increase of the bacterial 

 organisms. This explains the slow decay of matter 

 in soils during winter. Should the necessary 

 conditions not be present, the bacteria are unable 

 to flourish, and their place is taken by another 

 group, closely related, which bring about the 

 dissipation and waste of nitrogenous matter, known 

 as denitrification. 



Nitrifying organisms are far more abundant in 

 deeply cultivated and well aerated than in shallow 

 soils, hence the importance of thorough cultivation. 



1'nder the name Nitragin cultures have been 

 made of the various bacteria found in the root 

 nodules of Leguminous plants. Soils deficient of 

 these bacteria may have the solution containing 

 the cultivated bacteria added when the seed is 

 sown, as the cultures can be readily purchased 

 in the form of glass tubes. It is necessary to 

 sprinkle the mixture over the seed or distribute 

 it in the drills. 



for the rock garden, or a front 

 herbaceous border. Propagation, 

 division. Moist soil. 



Only Species : 



iilpinn, 3" to 5", spr. to 

 aut., wh. 



place in the 

 by seeds, or 



stylosa, 4", sum., Wen., 

 wh. to lil. (syn. Iberis 

 stylosa). 

 NOISETTIA. 



Noisettia longifolia is a dwarf-growing stove 

 evergreen tree (ord. Violariese), producing cream- 

 coloured flowers of no great beauty 



NOLANA. 



Annual or perennial, low-growing, often prostrate 

 herbs (ord. Convolvulaceas), sometimes with fleshy 

 leaves. They may be propagated by seeds sown in 



Nitta Tree (see Parkin africana). 



Noble Liverwort (tee Anenume Hepatica). 



