SCIENTIFIC HISTORY OF A PLANT. 



first great moving power. Vegetable physiology advances, and seems to incline to the idea 

 that the vitality of a plant is a purely chemical process. 



Upon what is dependent, then, this chemical action that enables a plant to decompose 

 both carbonic acid and water, that is always going on in it as a part of its life, and the 

 source of its development.^ The magnetic discoveries of Dr. Faraday of the connection 

 between magnetism, light, and cr^'stallisation, have no doubt brought us to the eve of a 

 great generalisation. We are in a state so happily described by Humboldt as " a state 

 of prcsagement" — in one of those intervals that renders the history of philosophy so in- 

 distinct between the presentiment of an epoch and its actual realisation. We have the 

 strongest grounds for considering galvanism, electricity, magnetism, as one and the same 

 force; whicn force is a certain quality of matter termed by Professor Graham polarity, 

 which is due to the presence of inherent magnetism. So then, we may almost go so fiir as to 

 say, that the same force that deflects a ray of polarised light — that causes the crystal to 

 elect a certain determinate position in the magnetic field — that gires polarity to the needle 

 of the compass — that this same force causes the formation and growth of an inorganic 

 cell. 



Such may be considered as an unfinished and imperfect glance at some of the most strik- 

 ing points in the chemical history of vegetation; but our survey is not yet finished. The 

 vegetable fiame requires the introduction of certain peculiar elements which are not organ- 

 ic, but which, nevertheless, makes it subservient for the support of life, and for the growth 

 of structure. 



We do not now wish to discuss the exact degree of alkalies or alkaline earths required 

 in certain cases, nor to trouble ourselves about the presence of organic acids in plants. We 

 know that oaks require certain conditions for their existence; in some soils they flourish, 

 in others they will not live. A barren and granitic soil amply supports the Pine and the 

 Fir, but not the Oak; and this because such soils do not contain sufficient alkalies for the 

 purpose. The Equisetacea3, like the Oak, require much potash; a soil formed from .the 

 grauwacke and porphyry, nourishes these plants. 



The Tobacco-plant and the Vine require lime; the Beet and Potatoes magnesia; Cheno- 

 podium likes nitrates; and the Fuchsia iodine; Cereals phosphates of ammonia and mag- 

 nesia. For the growth of the.se plants, one or other of these constituents is required; but 

 there are some soils composed of pure sand and limestone — they support no species of ve- 

 getation; they are absolutely barren. Argillaceous earths always exist in a fertile soil; 

 their fertility being doubtless derived from the alkali they contain, because rich soils were 

 formed by the disintegration of potash and soda felspars. Alumina is never found in the 

 ashes of plants; its action is merely indirect. It is useful in condensing the water and 

 the ammonia of the atmosphere. A cubic foot of felspar contains enough potash to sup- 

 ply an Oak-copse of twenty-six square feet with potash for five j^ears. 



We find, even in short excursions in our own country, great changes in the scenery of 

 different places; this is often brought about by the predominance of a certain class of 

 shrubs. We may pass a woody country — a country occupied as arable land — an entirely 

 pastoral country. Whence this differenee? From the soil, which influences the produc- 

 tions owing to the operations in nature of the f^icts which I have just stated. Soil, with 

 climate, is omnipotent in influencing the distribution of plants; and the formation of soil 

 and arable land is one of the main points of agricultural geology. Such a fact furnishes 

 us with a very clear example of the connection existing between chemistry, botany, and 



y- 



how are soils formed.? This is yet a question to be explained. 



