670 



HISTORY OF THE VEGETABLE KINGDOM. 



species, by engrafting, budding, and other pro- 

 cesses. 



Soil. The soil wliich covers tlie surface of 

 tlie earth, is composed of the pulverized matter 

 of the different rocks, the primary ingredients 

 of which are silex, alumina, lime, magnesia, iron, 

 and a few other salts. This is called the pri- 

 mary soil, and according as either of the com- 

 ponent ingredients preponderates, it may be 

 sandy, clayey, calcareous, ferruginous, saline. 

 The soil also contains a greater or less proportion 

 of vegetable remains, such as the decomposed 

 leaves and trunks of trees, or the peaty remains 

 of cryptogamio and other marsli plants. Some 

 soils, indeed, are almost entirely composed of 

 vegetable remains, and constitute the rich dark 

 mould, which, duly diluted, is esteemed the most 

 fertile for the gi'owth of vegetables. Some 

 plants, however, thrive best in one kind of soil, 

 and some in another. The object of the culti- 

 vator then, and especially of the horticulturist, 

 is to adapt his soil for the particular kinds of 

 plants he wishes to rear in perfection. Hence, 

 the preparation of artificial soils. It is doubted 

 by many, whether the pure earths afford any 

 nourishment to plants ; at all events, they enter 

 but very sparingly into their composition. They 

 serve, however, as a medium by which water, 

 carbon, and some of the gases, are conveyed into 

 their juices, and also as a convenient means by 

 which the fibrous or bulbous roots are attached 

 to, and held fiim and stationary in, the ground. 

 The true nourishment of plants is water and 

 decomposing organic matter, whether vegetable 

 or animal. The constituent parts of the soil 

 which give tenacity and coherence, a]'e the 

 minutely divided particles, and they possess this 

 power in the greatest degree if they be alumin- 

 ous. 



If the sUioious or sandy particles are in excess, 

 however, sterility is the consequence. Neither 

 must the soil be too much comminuted; a cer- 

 tain proportion of coarser particles seems to be 

 requisite. No one ingredient should be in excess 

 in any fertile soil, not even an excess of organic 

 matters : so that the best soil for general pur- 

 poses is that where an equable admixture of the 

 general ingredients is present, with a portion of 

 the particles In a state of minute comminution. 



Much of the fertility of soils depends upon 

 their power of absorbing moisture from the air. 

 When this power is great, the plant is supplied 

 with moisture in dry seasons, and the effects of 

 evaporation during the sunshine is compensated 

 by the absorption of moisture at night. Stiff 

 clayey soils which absorb a great proportion of 

 rain-water are not, however, the best suited for 

 absorbing it in dry weather, as the surface be- 

 comes hard and separates into deep fissures, whidi 

 assist the evaporating effects from the interior. 

 The best absorbing soils are those in which 



there is a due admixture of sand, clay, and lime, 

 with animal or vegetable matter, and of a loose 

 and light texture, freely pemieable to the air 

 and moisture. 



Carbonate of lime, and animal and vegetable 

 matter, are highly useful in this respect to soils : 

 they impart an absorbent power without giving 

 the soil too great tenacity. Tlie absorbent 

 power of soils ought to be adapted to the cli- 

 mate. In moist climates, a sandy light soil will 

 be more productive than a deep clayey one, and 

 the contrary. The subsoil also has a consider- 

 able effect in modifying the quantity of mois- 

 ture. Shallow soils, situated on rocky ground, 

 soon lose their moisture, while deep clay subsoils 

 retain it for a long time. 



Some soils absorb heat much more quickly 

 and copiously than others, and also retain their 

 heat longer. Black and brown mould has this 

 property, while lighter clays and chalky soils 

 are less absorbent of heat, the former giving it 

 out again sooner tlian the latter. 



Marshy soils, exposed to inundations and to 

 continual evaporation, are colder and more un- 

 genial than dry lands. The elevation above tlie 

 sea level has also a very great effect on the tem- 

 perature and on the growth of plants. 



Digging, ploughing, and pulverizing the soil, 

 and exposing the surface to the action of the 

 summer sun and the winter's frost, are highly 

 useful operations, by which the tenacity of stiff 

 soils are overcome, weeds and insects are destroy- 

 ed, and a quantity of air is admitted into its par- 

 ticles. 



The rotation of crops is a well known prac- 

 tice among all vegetable cultivators. In order 

 that vegetables may thrive vigorously, and be- 

 come productive, it is necessary that their locali- 

 ties should be changed every other year. This 

 is the case with the grains and many other plants, 

 but does not take place with all vegetables, nor 

 trees -which are long lived. At one time it was 

 supposed that vegetables exhausted the nutritive 

 particles of the soil, if grown too long on one 

 spot, and thus required a change ; but as other 

 vegetables requiring precisely the same kind of 

 nutrition, are found to grow perfectly well if 

 planted in succession to their predecessors of 

 another kind, this theory was not deemed tena- 

 ble. The prevailing theory now is, that plants 

 give out from their roots an excrementitious 

 matter, which, though noxious to individuals of 

 the same species, may not be so to other fami- 

 lies of plants. The experiments of M. Macaire 

 demonstrate that plants do excrete noxious mat- 

 ters from their roots, perhaps analogous to the 

 excrementitious matter of animals.* 



Manure. The use of manure is to afford a 

 supply of nutritive matter to plants. It lias 



• Edin. Philosopli. Jom-nal, No. 28, p. 1\h. 



