Hints on Vegetation. 1 1 



cultivation ; substances must be frequently renewed, in order to re- 

 store to the soil, materials which have been absolutely consumed in 

 the process of vegetation. 



In regard to those saline substances, on the advantages of which 

 some authors have laid so much weight, it does not appear that salt 

 is essential to the growth of any species of plants, the marine alone ex- 

 cepted ; and there are many productive soils, in which little or no salt 

 can be traced. Salt however, though noi essential, is of use to ve- 

 getation. It may operate upon plants, as it does upon the human body, 

 by assisting to digest the food, without furnishing nutriment itself, it 

 is of use, mixed with dung, as an assistant to putrefaction. In fact, it 

 promotes vegetation, as mustard, ginger, &c. are useful in human food, 

 contributing to render other things nutritious, by exciting action in 

 the stomach and other organs of digestion and assimilation. It is 

 also serviceable by attracting moisture, destroying vermin in the soil, 

 and putrefying the roots of weeds or other plants which it first en- 

 counters, by which nourishment to the succeeding ones is supplied. 



6. Cultivation. The culture of the earth is essentially necessary 

 for the growth of plants to perfection. By dividing the particles of 

 the soil, the roots can more easily penetrate it, and they can more 

 readily suck in the moisture and nourishment which it contains. By 

 proper culture also, weeds, or useless plants, are extirpated, whilst stir- 

 ring the earth, admits more air and moisture to those which have been 

 sown. Young trees certainly thrive much better, if the soil in which 

 they are planted, has been previously ploughed so deep, as readily to ad- 

 mit their roots and suckers. Even after they have been planted, it is of 

 service to cultivate potatoes, and other roots, among the young plan- 

 tations. 



2. Of the Agents which are destructive or injurious to 

 Vegetation. 



The obstacles to vegetation which it is necessary here to discuss 

 are, mineral, or noxious substances in the soil, and vermin. 



1. Mineral or noxious substa?ices in the soil. There are cer- 

 tainly many substances in the soil, noxious to vegetation, in parti- 

 cular those of a metallic nature. Where mines of iron, lead, or cop- 

 per are near the surface, many plants will not grow to perfection, 

 which is known to be the case at the Lead Hills in Scotland, &c. 

 Clay-slate, shale or till, in which there is a great deal of iron and alum, 

 is so unfavourable to vegetation, that any considerable quantity of 

 it would destroy the fertility of the richest soil. Fallowing, or expo- 

 sure to the air, and the use of lime, will, it is supposed, correct the 

 noxious qualities of those substances. 



There is also an astringency or acidity in peat, so injurious to vege- 

 tation, that until any quality of that nature is subdued, though that 

 species of soil is a mass of vegetable matter, yet nothing but heath, 

 and other useless plants will grow in it. 



2. Vermin. Plants are also much injured, by the various sorts of 

 vermin with which both the earth, and the air, abound. Those 

 which inhabit the earth, it is supposed, may be destroyed by salts, by 



