336 APPLICATION- OF PKINCIPLES. 



Doubtless one of the safest rules for a gardener, in 

 determining the soil required for a given plant, would 

 be, if practicable, to ascertain what amount of mineral 

 matters it contains, and to select earth in which those 

 substances abound. For, although it may be asserted 

 that the presence of iron, copper, or other substances, 

 in plants, in minute quantities, is accidental and un- 

 important, yet such a supposition is gratuitous, if not 

 altogether unfounded ; fori do not know what war- 

 rant we have for saying that any of the constant 

 phenomena of nature, however minute they may seem 

 to be, are accidental. This at least is certain, that, 

 where mineral substances occur abundantly in plants, 

 they are part and parcel of their nature, just as much 

 as iron and phosphate of lime are of our own bodies ; 

 and we must no more suppose that grasses can dis- 

 pense with silica in their food, or marine plants with 

 common salt, than that we ourselves could dispense 

 with vegetable and animal food. Flint is found on 

 the exterior of the whole Graminaceous order, with- 

 out exception ; it forms the polished surface of the 

 Cane Palm, the grittiness of many kinds of timber ; 

 sulphur abounds in Cruciferous plants, especially 



of the New Jersey marl, when we consider its chemical composition. 

 According to the numerous analyses of Mr. Rogers, the marl from 

 various localities contains from 9 to nearly 1 3 per cent of potash, 

 and seldom more than one-half per cent, of lime: and Mr. Rogers* 

 very correctly states "that the true fertilising principle in marl is 

 not lime but potash." On this subject see the note commencing on 

 p. 337. G.] 



* Final Report on the Otology of the State of J^ew Jertty; by Heniy D. Boferli 

 1840. 



