THE SOIL MUST CONTAIN WHAT THE PLANT REQUIRES. 181 



quantity as easily to yield to the crop so much of each as the hind of plant 

 specially requires. And if one of these necessary inorganic forms of 

 matter be rare or wholly absent, the crop will as certainly prove sickly 

 or entirely fail, as if the organic food supplied by the vegetable matter 

 of the soil were wholly withdrawn. It is, therefore, as much the end of 

 an enhghtened agricultural practice to provide for the various require- 

 ments of each crop in regard to inorganic food, as it is to endeavour to 

 enrich the land with purely vegetable substances. 



Since, also, as above shown, not only the relative quantity of inor- 

 ganic matter, but its kind or quality, likewise, is different in different 

 plants, — it may be, that a soil on which one crop cannot attain to ma- 

 turity may yet surely and completely ripen another — a fact which is 

 proved by every-day experience. The soil, which is unable to supply 

 with sufficient speed all the lime or the potash required for one crop, 

 may yet easily meet the demands of another, and afford an ample re- 

 turn to the husbandman when the time of harvest comes.* 



On the other hand, this consoling, at once, and stimulating reflection 

 must arise in the mind of the practical agriculturist from the considera- 

 tion of the above facts — that if the soil contain all the inorganic substan- 

 ces required by plants, and in sufficient quantity, it will grow, if rightly 

 tilled, any crop which is suited to the climate, — or conversely to make 

 it capable of growing any crop, he has only — along with his usual sup- 

 plies of animal or vegetable matter — to add in proper quantity these in- 

 organic substances also. • 



Here a crowd of questions cannot fail to start up in your minds. You 

 will ask, for example, 



1°. What are the several inorganic substances usually present in 

 cultivated plants, and what their respective proportions ? 



2°. Which of them are most generally present in the soil? 



3°. In what form can those which are less abundant be added most 

 easily, most advantageously, and most economically ? 



We shall consider in succession these, and along with them other 



• On the same principle, also, some of the interesting facts connected with the grafting of 

 trees are susceptible of a satisfactory explanation. 



The root of a tree selects from the soil the kind and gwaZiVi/ of inorganic matter which 

 are required for the healthy maturity of its own parts. Any other tree may be grafted on it, 

 which in its natural state requires the same kind of inorganic matters in nearly the same 

 proportion. This is the case generally with varieties of the same species— more rarely 

 with trees or plants of different species— and least frequently with such as belong to differ- 

 ent genera. The lemon may be grafted on the orange, because the sap of the latter con- 

 tains all the eartliy and saline substances which the former requires, and can supply tliem 

 in sufficient quantity to the engrafted twig. But the fig or the grape would not flourish or 

 ripen fruit on the same stock — because these fruits require other substances than the root of 

 the orange cares to extract from the soil, or in greater quantity than the sap of the orange 

 can supply them. 



It is not for want of organic food, for of this the sap of nearly all plants i<3 full — and we 

 have seen in our previous lectures, how the sugar of the fig, the tartaric acid of the grape, 

 and the citric acid of the lemon, may all be produced by natural processes from the same 

 common organic food. When we plant a tree or sow a crop on a soil which does not con- 

 tain all that the tree or crop requires, the tree must slowly perish, — the crop cannot yield a 

 profitable return. So it is in grafting. l\e sap of the stock must contain all that t/ie engrafted 

 bud or shoot requires in every stage of its growth. Or to recur to our former illustration — 

 if the potash or lime required by the grape be not taken up and in sulTicient quantity by 

 the root of the orange, it will be in vain to graft the former upon the latter with the liope of 

 Us coming to maturity or yielding perfect fruit. 



This principle may also serve to explain many other curious and hitherto obscure cir- 

 cumstances connected with the practice of the gardener. 



