144 INFLUENCE OF SALINE SUBSTANCES AND MAKTJRES. 



locity with which the bamboo, the palm, the tree fern, and other vascu- 

 lar plants, may grow in tJieir native soil and climate. And with what 

 numerous and complicated chemical changes is the production of every 

 grain of the substance of these plants attended — how rapidly must tlie 

 food be selected and absorbed from the air and from the soil — Iiow 

 quickly transformed and assimilated ! 



The long period of time during which, year after year, these changes 

 may proceed in the same living vessels, or in the same tree, is no less 

 wonderful. Oaks have lived to an age of 1500 or 2000 years — yew 

 trees to 3000 years — and other species are mentioned as having flour- 

 ished from 4500 to 6000 years ; while even a living rose tree {rosa 

 canina) is quoted by Sprengel as being already upwards of 1000 years 

 old. — [Sprengel, Lehrc vom Diinger, p. 76.] 



Tlie rapidity of tbe growth of a plant, and the length of its life, are 

 equally affected by circumstances. On a knowledge of these circum- 

 stances, and of the means of controlling or of producing them, the en- 

 lightened practice of agriculture is almost entirely dependent. 



Over the natural conditions on which vegetation in general depends, 

 we can exercise little control. By hedge-rows and plantations we can 

 sheher exposed lands, but, except in our conservatories and hot-houses, 

 the plants we can expect to cultivate with profit will always be deter- 

 mined by the general climate in which we live. So the distribution of 

 rain and sunshine are beyond our control, and though it is ascertained 

 that a thundery condition of the atmosphere is remarkably favourable to 

 vegetable growth, [Sprengel, Lehre vom Diinger, p. 73], we cannot 

 hope that such a state of the air will ever be induced at the pleasure or 

 by the agency of man. But under the same natural conditions of cli- 

 mate, there are many artificial methods by the use of which it is within 

 our power to accelerate the growth, and to increase the produce, of the 

 most valuable objects of ordinary culture. 



Thus the germination of seeds in general is hastened by watering with 

 a solution of chlorine (Davy), or of iodine or bromine (Blengini), and 

 Davy found that radish seed which germinated in two days when wa- 

 'ered with solutions of chlorine or sulphate of iron, required three when 

 (vatered with very dilute nitric acid, and five whh a weak solution of 

 sulphuric acid. 



It is familiarly known also in ordinary husbandry, that the applica- 

 tion of manures hastens in a similar degree the development of all the 

 parts of plants during every period of their growth — and largely increases 

 •he return of seed obtained from the cultivated grains. Ammonia and 

 its compounds likewise, and nitric acid and its compounds, with many 

 Dther saline substances existing in the mineral kingdom and occurring in 

 soils, or which are produced largely in our manufactories, have been 

 found to produce similar effects. 



It would be out of place here to enter upon the important and interest- 

 ing field opened up to us by a consideration of the influence exercised 

 by these and other substances, in modifying both in kind and in degree the 

 chemical changes which take place in living vegetables. The true mode 

 of action of such substances — their precise eflects — the circumstances 

 under which these effects are most certainly produced — and the theoreti- 

 cal views on which they can be best accounted for — will form a subject of 

 special and detailed examination in the third part of the present lectures. 



