VEGETABLE CULTURE 127 



To demonstrate the presence of proteid, we may therefore crush 

 succulent vegetable tissue, filter the expressed liquid into a test 

 tube and warm, when a whitish precipitate will be produced. The 

 mineral substance of plants is contained in their ashes, part of which 

 is soluble in water and part (carbonate of lime, etc.) insoluble. 



To grow heavy crops of vegetables of good quality the con- 

 ditions of moisture, temperature, aeration, presence of mineral 

 food in an available form, and absence of injurious substances 

 from the* soil, must be met. The ground must therefore be 

 trenched, unless this has been done in the previous year, and 

 well manured. The best manure is farmyard manure, this being 

 a general manure ; that is to say, it contains, either in an 

 immediately available form or in a form which will gradually 

 become available within a few months, those three chemical 

 elements which are essential to plant life and are shown by 

 experience to be easily removable from the soil. These three 

 elements are nitrogen, phosphorus, and potassium. The four 

 remaining elements (sulphur, iron, calcium, and magnesium) 

 are in practically all cases present in sufficient quantity. Apart 

 from the fact of its being a general manure, farmyard manure 

 keeps a heavy soil open, and thus ensures the presence of air 

 and the passage of water. When partly decomposed under 

 the action of soil bacteria, it gives rise to a dark, powdery 

 substance termed humus, which possesses the property of retain- 

 ing moisture, and consequently farmyard manure is equally 

 valuable from its physical effect on light sandy soil. Stable 

 manure is drier and more easily fermentable than manure from 

 the cowshed or pigstye. The former is therefore the most suitable 

 for very heavy soils, and the two latter for sandy soils. For 

 intermediate types of soils the difference in the behaviour is so 

 slight as to be negligible. A soil which has not previously been 

 used as a garden ground, or, having been so used, is in poor 

 condition, should receive a heavy dressing of farmyard manure. 

 For farm purposes, twenty tons per acre is an average dressing. 

 For a garden, the soil of which is poor, this amount may be doubled. 

 The ordinary two-wheeled farm-cart will hold about a ton of 

 farmyard manure, and this, therefore, is the quantity which 

 may be applied to every four rods of the garden. This will be 



