104 



SIR H. DAVY S AGRICULTURAL CHEMISTRY. 



in combination with this metal. By the 

 same method, Sir H. Davy decomposed 

 strontites and magnesia; and, by submit- 

 ting silex, alumine, zircon, and glucine 

 to the action of the galvanic battery, in 

 fusion wit h potash or soda, or in contact 

 with iron, or by fusing them with potas- 

 sium and iron, appearances were obtain- 

 ed sufficiently indicative of their decom- 

 position, and of the production of bases 

 of a metallic nature. Thorina, the last 

 discovered earth, was decomposed by 

 heating the chloride of thorium with po- 

 tassium. The metallic bases of the earths 

 approach more nearly than those of the 

 alkalies to the common metals, and the 

 earths themselves have a stricter resem- 

 blance than the alkalies to metallic ox- 

 ides. Viewing them as forming part of 

 a natural arrangement, they furnish the 

 link which unites the alkalies to the me- 

 tals. Accordingly, many of the more 

 recent systems of chemistry treat of all 

 these bodies as forming a single group, 

 under the name of the metallic class. 



Still (as Dr. Ure justly remarks,) what- 

 ever may be the revolutions of chemical 

 nomenclature, mankind will never cease 

 to consider as earths, those solid bodies 

 composing the mineral strata, which are 

 incombustible, colorless, not convertible 

 into metals by all the ordinary methods of 

 reduction, or, when reduced by scientific 

 refinements, possessing but an evanescent 

 metallic existence. — Encyc. Amer. 



SIR H. DAVY S AGRICULTURALCHEMISTRY. 



(Coiitiiim.d from page 9fi, No. 6.) 



It has been shown by the experiments 

 of Mr. Knight, and those made by other 

 physiologists, that the sap descending 

 through the bark, after being modified in 

 the leaves, is the principal cause of the 

 growth of the tree; thus, if the bark is 

 wounded, the principal formation of new 

 hark is on the upper edge of the wound, 

 and when the wood has been removed, 

 the formation of new wood takes place 

 immediately beneath the bark : yet it 

 would appear from the late observations 

 of M. Palisot de Beauvois, that the sap 

 may be transferred to the bark, so as to 

 exert its nutritive functions, independent 

 of any general system of circulation. That 

 gentleman separated different portions of 



bark from the rest of the bark in several 

 trees, and found that in most instances 

 the separated bark grew in the same 

 manner as the bark in its natural state. 

 The experiment was tried with most suc- 

 cess on the lime tree, the maple and the 

 lilac; the layers of bark were removed 

 in August, ISIO, and in the spring of the 

 next year, in the case of the maple and 

 the lilac, small annual shoots were pro- 

 duced in the parts where the bark was 

 insulated. 



The wood of trees is composed of an 

 external or living part, called alburnum 

 or sap-wood, and of an internal and dead 

 part, the heart-wood. The alburnum iS 

 white, and full of moisture, and in young 

 trees and annual shoots it reaches even to 

 the pith. The alburnum is the great 

 vascular system of the vegetable through 

 which the sap rises, and the vessels in it 

 extend from the leaves to the minutest 

 filaments in the roots. 



There is in the alburnum a membranous 

 substance composed of cells which are 

 constantly filled with the sap of the plant, 

 and there are in the vascular system 

 several different kinds oi tubes. Mirbel 

 has distinguished four species, the 5/my;/e 

 tubes, the porous tubes, the tracheas, and 

 the false tracheae. — The tubes, which he 

 has called simple tubes, seem to contain 

 the resinous or oily fluids peculiar to 

 different plants. 



The porous tubes likewise contain these 

 fluids; and their use is probably that of 

 conveying them into the sap for the pro- 

 duction of new arrangements. 



The tracheae contain fluid matter, which 

 is always thin, watery, and pelucid, and 

 these organs, as well as the false tracheae, 

 probably carry off water from the denser 

 juices, which are thus enabled to con- 

 solidate for the production of new woods. 



In the arrangement of the fibres of the 

 wood, there are two distinct appearances. 

 There are series of white and shining 

 laminte which shoot from the centre 

 towards the circumference, and these con- 

 stitute what is called the silver grain of 

 the wood. 



There are likewise numerous series of 

 concentric layers which are usually called 

 the spurious grain, and their number 

 denotes the age of the tree. 



