SCIENTIFIC HISTORY OF A PLANT. 



constituent, and that for the most part soils are formed by the disintegration of the parent 

 rock of the district, it is obvious that these facts, when applied on a great scale to nature, 

 must divide and influence vegetation; for according to the geological conformations of a 

 country is its soil, and so is its flora. 



The subsoil is generally in connection with the original rock, by fl"hose wearing away it 

 was formed, and the soil is in intermediate relation to it, not always having even the same 

 color; fur it may be a transplanted soil, or separated from the parent rock by a larger 

 amount of gravel, in which case the white subsoil from the chalk, or the yellow from the 

 clays, would not represent the color of the land's exterior surface. The depth, texture, 

 and fertility of a soil is dependent both upon the mineral constituents and the easily dis- 

 integrating properties of the rock whence it is formed; and it is the pliysical and nnneral, 

 more tlian the geological age of a soil, that conduces to its fertility: old rocks maybe bar 

 ren in one place, but fertile in another. 



In merely a geological survey of a soil we are apt to underestimate, if not to overloook, 

 the important fact, which is played by water in vegetation. Yet, if we cast our eyes over 

 a hydrographic map of the world, we find certain rainless districts, destitute of water 

 courses, and where the air is rarified to allow of the condensation of aqueous vapor. 

 What do travellers tell us of the vegetation of a tract of country so circumstanced? AVhy, 

 in tliis rainlesss desert let but a little spring of water rise, it generates fertility in the li- 

 mited sphere of its operations; an oasis is produced; and that arid ocean of burning .sand 

 rejoices in one small island of vegetable life. 



Water is one local cause of influencing the fertility of a soil, but there are various oth- 

 ers, many physical actions in one place shifting the superficial detritus which covers the 

 more stubborn rocks; and if we do not take circumstances like these into account, we 

 shall be apt to consider that geology gives us more information than it really does; to form 

 the idea, tliat with a geological map before us, it would be no trouble by its inspection ac- 

 curately to ascertain the soil of any particular country. 



The mill-stone grit plains around Paris in a geological map of the district, would be si- 

 milarl}' colored; yet each one of these plains has its own particular form of vegetation. 

 Montmorency is covered with corn-fields; Sannois supports only a short sterile rod; Meu- 

 don is furnished with Spanish chestnut trees; the Airaflexuosa, theMelampyrum sylvati- 

 cum, the Pteris aqiiilina, all grow there. Only a minute's inspection clears up this seem- 

 ing incongruity. We find, though no difference is pointed out by the map — for geologi- 

 cally speaking, there can be no distinction made: they are all mill-stone grits — we find in 

 the one case the millstone-grit is mixed with sand; in another case it is mixed with clay; 

 and, in the third, it is alone and uncovered. 



Thus far we have pursued our journej'', and now it is time that we pause. I would hope 

 that my sketch has been clearly followed, and that my design, imperfect as it is, has been 

 strictly adhered to. 



In following the chemical history of a plant, we saw how interwoven were a variety of 

 subjects with each other; we saw, too, that the plant itself is capable of reading to us 

 many a lesson from the great book of nature, of bringing before us many of her beautiful 

 operations; of exhibiting to us clearly and distincly some fuller proofs of that design, and 

 order, and harmon}', so palpably jnanifested in this our universe. 



So then man and nature can be viewed as two great forces here, the one progressive, and 

 the other stationary, albeit, though not still, yet both working out their proper ends in 

 the universal scheme of the Great Designer, which it is past the feeble ken of man 

 netrate 



