THE NITROGEN COMPOUNDS IN PLANTS 155 



of lime in the soil should not be less than } per cent., and not 

 more than 2 per cent. 



The manures used contain a high percentage of potash, 

 but no large amount of phosphates. The fields on which 

 tobacco is planted out must be well sheltered from wind. 

 Tobacco may be substituted for potatoes or other crops in 

 the rotation or can be grown several years successively. 

 On the continent phosphates are not usually applied direct 

 to the tobacco, the previous crop in the rotation having 

 already received heavy dressings of phosphates in advance. 

 Chlorides are considered bad for the development of the plant. 

 Compound manures containing about 5 per cent, nitrogen, 

 17 per cent, soluble phosphate, and 7 per cent, potash are 

 considered very suitable for this crop, which corresponds 

 roughly to about one part of sulphate of potash, two parts 

 of sulphate of ammonia, and four parts of super-phosphate. 

 Kainit should not be used since it contains too much chlorine. 

 The plant is usually grown on low, flat drills, very frequently 

 being planted out in the furrow, and subsequently earthed 

 up. The seed is generally sown about the middle of March 

 or April in hot beds. The suckers and lateral growth should 

 be broken off, and the plant allowed to bear ten leaves. 

 The better qualities are not harvested all at once, but plucked 

 leaf by leaf. They are then dried, and taken to curing 

 barns, in which ventilation is an important point. The first 

 process consists in wilting the leaves, when they lose moisture, 

 and become limp, but the drying should not take place too 

 fast. The second process is that of yellowing the leaf. 

 This subsequently turns to brown, and the leaf becomes 

 fairly well dried. Then drying must proceed fairly rapidly, 

 in order to prevent mould setting in. About one half of 

 a ton of dry tobacco per acre represents the ordinar^^ 

 yield. 



In tropical climates a rich, sand}^ loam is preferred, 

 containing coasiderable quantities of potash and lime. 

 In India a great many of the most suitable districts contain 

 well waters with nitrates in solution, which are used for 

 irrigating purposes. The land is usually thoroughly ploughed 



