THE FARMER'S MAGAZINE. 



213 



KENNINGTON AGRICULTURAL AND CHEMICAL COLLEGE. 



LECTURES ON THE GENERAL PHENOMENA OP THE EARTH, HAVING REFERENCE TO THE 

 PRODUCTION AND MAINTENANCE OF ORGANIC LIFE. 



BY CHARLES JOHNSON, ESQ., PROFESSOR OF BOTANY, GUY'S HOSPITAL. 



Lecture XIII. 



While the minuter forms of the Alga are continually em- 

 ployed in preparing their aquatic abode, whether sea or river, 

 lucid lake or turbid pool, for the developmf nt of higher grades 

 of vegetable life, parallel creations on the land are equally 

 active to a similar end, working alike unseen, and even un- 

 suspected in the earliest fulfilment of their functions. These 

 are the Lichens, the first in our classification of terrestrial 

 plants, and the natural precursors of the groups which follow 

 on the scale. The cause of their first appearance, in any par- 

 ticular locality, is as much of a mystery to the human observer 

 as is that of their aquatic brethren ; though, as in the case of 

 the latter, their after-propagation is the result of laws, the 

 action of which is generally recognized in vegetation of a 

 higher gr?de, however insufficient theory may yet have proved 

 to its elucidation. 



Let us examine the history of Lichen production and suc- 

 cessional development — not critically, and under the influence 

 of philosophical prejudices, which too often tend to lead us to 

 false conclusions, but, as it may be read on the page of Nature. 

 A newly-bared surface of rock, or sand, or soil, a brick or tile, 

 nay, even a pane of glass, exposed to air and light, becomes 

 the resting-place of myriads of microscopic atoms, which en- 

 large and multiply their kind ; that kind is the simplest 

 organism imagined or recognized by human senses : it is the 

 cell again ; the cell is the plant itself, developing the cell its 

 germ, its beginning and its end the same. Such is ever vege- 

 tation in its earliest appearance, where organic elements are 

 wanting for the production of a higher or more complicated 

 frame ; and our microscopic atoms are the first colonizers of 

 the hitherto barren spot of earth — the pulverulent Lichens. 

 We may pause awhile, to speculate as to whence they come. 

 The minuteness of the germs — (seeds we will call them, though 

 the botanist may cavil about the term) — of these little plants, 

 is such, that the lightest movement of the air may dislodge, 

 and bear them to incalculable distances ; and, without 

 exaggeration, we may assume that, like the moisture which is 

 mingled with the atmosphere as viewless vapour, they may be 

 constantly present throughout its whole expanse, be inhaled 

 with our breath, and distributed with every wind that blows. 

 I am not, in this assumption, violating the compact just made, 

 at the commencement of the present paragraph, to avoid for 

 the mOtiient all mere theory, and examine fact as it exists, alone 

 and without bias. The origin of a living being is required ; 

 and when we note the successors of such being making their 

 appearance under circumstances of universal operation, we are 

 justified in seeking a corresponding source for itself. The 

 docirine, ascribing the apparently spontaneous development of 

 individuals, belonging to the lowest classes of vegetation, to 

 this constant presence of their seeds floating in the atmos- 

 phere, cannot he proved to demonstration ; but when we learn 

 that certain of the simpler forms of fungus, as mould, &c., are 

 found in the diseased tissues of living animals, and only upon 

 such as are exposed to contact with the air, as upon the sur- 

 face of their bodies, or in the air-cells and tubercular cavities 

 in the lungs, as well of mankind as of the inferior animals, 

 their origin surely is too evident to admit of misconception : 

 wherever seen, they are the produce of 8\ich air borne germs, 

 which require only a resting-place to commence the career of 

 growth and reproduction. 



Linna;u9, comparing, in a fanciful mood, the aspects and 

 functions of the individuals composing the great natural fami- 

 lies of the vegetable kingdom with the several grades of human 

 society, bestowed the Latin title of YernncuU, or bond-slaves, 

 on the Algffi ; under which denomination he included both the 

 plants 80 called by modern botanists, and the Lichens, the re- 



lative structures of which seem to have been prefigured in hia 

 miud at a veriod when microicopic research had yet done little 

 or nothing towards the elucidation of such resemblances. The 

 title is, as observed by the late Professor Gilbert Buniett, of 

 King's College, Loudon, peculiarly appropriate to the Lichens, 

 " which are, as it were, chained to the soil they labour to im- 

 prove for the benefit of others, though from it they derive no 

 nourishment themselves." The latter assumption is, in most 

 instances, probably incrrect, as may appear from our coming 

 inquiry ; a circumstance, however, that does not greatly inter- 

 fere with the justness of the comparison. 



The modern system of farming by rotation crops, supersed- 

 ing the antiquated process of fallowing, is only the adoption 

 of principles constantly in action under the government of 

 Nature ; and the history of the little plants before us strongly 

 exemplifies a fact, of which our stubborn ancestors, and even 

 mauy of their less-informed successors, were !oi g in becoming 

 convinced, namely, the influence of the unseen and intactible 

 upon the visible and tangible. The necessity of accumulating 

 the proximate elements belonging to the higher forms of life, 

 before the introduction of the latter upon the face of the 

 world, has been already remarked upon, in one of our previous 

 lectures ; and where are the constituents of these compounds, 

 the true elements, to befound? whence are they to be elaborated, 

 but from the rock, the air, and the watei, each in itself incom- 

 petent to their necessary elaboration ! Life must precede 

 life. This is the grand law under which organic being, once 

 produced, can alone be maintained ; a law enunciated when 

 creation was an act, and which has remained such since that 

 act was fulfilled. No chemical manipulation of the inorganic 

 atoms of the fire-tempered granite or greenstone produces 

 the required compounds of animal and vegetable substance ; 

 the vital principle alone bein? capable of adjusting their pro- 

 portions, modifying their affinities to such a purpose, and 

 eliciting the mysterious combinations. The modern practi- 

 tioner in that glorious art, which seems to sport with the ele- 

 ments of simple matter, bidding them unite and separate at 

 will, fails in this. True ! he can arrange and disarrange the 

 organic atoms, force them to assume a different form, and, so 

 long as they remain organic, control results, even as he acta 

 upon the mineral ; but he has no producing power. He may 

 call forth the starch, the sugar, that did not exist as such be- 

 fore ; nay, even the odours of the rose and of the violet, where 

 no flowers are at hand to yield them. But, the products of 

 organization, that are here his playthings, are only compelled 

 into action under their own affinities with surrounding 

 matter; and those affinities, once overcome, once unbound, 

 his power over them as organic elements ceases, and a re- 

 newed subjection to the laws of life alone can restore them to 

 their former condition. . . 



In contributing to this recurring change and recompositiou, 

 every member of both animal and vegetable kingdoms is con- 

 stantly and actively employed, as a necessary consequence of 

 its existence. But, their mutual operations are too compli- 

 cated to admit of separate examination, beyond the point of 

 commencement, and a few stages upward upon the scale. Ou 

 the land, the lichen is, as heretofore remarked, the earliest 

 perceptible agent. But it may be inquired, What is a lichen ? 

 The question is as simple and pertinent aa mightbe.What is a 

 grass, a flower, or a tree? but is less easily answered so as to 

 be satisfactory to the uninitiated. The botanist defines a 

 lichen to be a " perennial plant, often spreading over the sur- 

 face of the earth, or rocks, or trees, in dry places, in the form 

 of a lobed and foliaceous, or hard and crustaceous, or leprous 

 substance, called a thallus, &c., &c." Will this definition 



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