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THE FARMER'S MAGAZINE. 



of organic productions inhabits the waters ; to some of the 

 simpler forms of which I have already alluded, as exem- 

 plifying the lowest observable grades of vegetable life. The 

 collective term Algse, employed by botanists to denominate 

 these, includes, however, a host of species, that from mei-e 

 cellular points vary to simple or branched filaments, and 

 thence to broad leaf-like expansions and even gigantically- 

 elongated stems, the latter often bearing prefigurations of 

 organs familiar to us in the highest grades of vegetable 

 life. To the inexperienced observer, no relation would 

 seem to exist between these aquatic organisms and the 

 lichens, and the parallelism above-mentioned might appear 

 utterly without foundation ; but, structurally considered, 

 they approach so nearly, in many instances, as even to 

 render plausible the supposition, noted in the previous 

 lecture, that their spores or seeds may be so for really 

 identical, as to render their production in the one or the 

 other form dependent upon the character of the medium in 

 which they vegetate. However disinclined we may be to 

 cherish such an assumption, the resemblance must be ad- 

 mitted; and, farther, the possibility that the alga and the 

 lichen commenced, as they now pursue, their ministry 

 simultaneously^, as preparatory to the grand process of 

 maintenance to those above them. At what geological 

 epoch their forms first appeared we have no means of deci- 

 ding. Textures so fragile and fugitive, so minute and 

 obscure, as those of their lower grades, have not survived 

 the process of fossilization ; a. process which, in the animal 

 kingdom, while it has preserved for our examination the 

 bone, the shell, and the coral, has been incompetent to 

 retain the softer tissues which these accompanied. Hence 

 only a few doubtfully-recognizable algaceous plants are met 

 with in the earlier fossiliferous rocks, and those of the 

 larger and more conspicuous grades; while of lichens 

 scarcely a trace exists. The absence of the remains of such 

 vegetables is, however, as previously stated, no proof of 

 their not having been present in the primeval seas, and 

 adhering to the yet-unabraded surface of the granitic peaks 

 by which their waters were first divided. 



In enumerating above the great natural groups, I have 

 noticed the terrestrial forms only, not admitting the algse 

 into the series, they being peculiarlj' the vegetation of the 

 waters, and in this respect opposed to every other produc- 

 tion of the vegetable kingdom ; of whicli the species, most 

 essentiall}' aquatic, belonging to other groups, require, more 

 or less constantly or periodically, the direct inlluence of the 

 atmosphere for the fulfilment of their vital functions. Their 

 colonizing influence is not so open to our observation as is 

 that of their terrestrial parallels ; but they fulfil offices of 

 such vast importance in the maintenance, on a broad scale, 

 of all organic life, as to claim, perhaps, even a more especial 

 notice of their agency. In the introduction to my descrip- 

 tions of the species found in the British seas, in the second 

 edition of " English Botany," the general history of this 

 interesting series of plants has been sufficiently developed 

 to answer our present purpose, both as regards their diver- 

 sified structure and value in the economy of Nature ; nor 

 can I better fulfil the end in view, than by adopting tJie 

 same, with such slight alteration as the nature of the subject 

 before us may require. 



Contrary to the habit of the lichens, many of which 

 dwell on the driest and apparently most inappropriate spots 

 for maintaining vegetable life, the algfe grow almost univer- 

 sally submersed ; a few only of the simpler kinds vegeta- 

 ting on damp ground, rocks, and walls, and these always in 

 situations where water is present, either accumulated or 



transfusing : it is the element of their existence. As before 

 alluded to, their simplest observable forms appear as single 

 cells of exceeding minuteness, consisting of a delicate trans- 

 lucent membrane, filled with a fluid or mucous matter and 

 innumerable little, coloured granules ; the granules enlarge 

 gradually, and eventually burst the including membrane, 

 becoming the sporules or seeds of the succeeding genera- 

 tion : such are the species which seem at present to consti- 

 tute the lowest extremes of organization. The little cells 

 in question, here regarded as distinct existences, are often 

 found, like those of the Protococcus or red-snow plant 

 described in the tenth lecture, scattered promiscuously 

 upon a thin film of slimy or gelatinous substance. 



Another series, higher on the scale of structure, is seen in 

 those fiuely- pencilled or filamentous plauts that form eo large 

 a proportion of the more brilliant and beautiful examples of 

 marine vegetation. la mas y of these, which are composed of 

 vesicles placed end to end in indefinite lines, the microscope 

 discovers each filament to be invested by a transparent film, 

 so that the condition of such a plant might be represented, not 

 unaptly, by suspending a necklace of hollow beads withiu a 

 glass tube. This tube in the living plant is glutinous, and 

 occasions most of the more delicate kinds of sea-weed to adhere 

 firmly to paper in drying. A similar coating is found upon 

 the larger and more complicated species, in which it may be 

 considered to prefigure the cuticle or outer covering of skin 

 that invests the surface in the higher order of plauts. Thia 

 transparent tub:?, which gives a continuous or even surface to 

 the otherwise jointed, hair-like stems and branches of a Con- 

 ferva, accords so nearly in appearance and composition with 

 the exjpanded film upon which the cells of Protococcus and 

 several of its allies are found reposing, that there is no slight 

 reason for believing them primordially similar, and that they 

 only difier iu consequence of the different degrees of vital 

 energy regulating the growth of then: respective cells, which 

 where separate, are too feeble to overcome the inertia of the 

 substance on which they are generated ; but where combined, 

 convert it by their greater assimilative power into a protective 

 cover. 



A third great natural division of these plants includes the 

 larger kinds of sea-weeds, through the several grades of which 

 the cellular structure is capable of being traced to the most 

 elaborate and complicated forms of which it is susceptible. In 

 these the cells become aggregated in breadth as well as in 

 leugth, constituting broad leafhke expansions and cylindrical 

 or flattened stems aud branches. . 



The modes of reproduction in the higher algse are greatly 

 diversified, so far as external appearances are concerned, though 

 in reality the germs themselves seem to be of corresponding 

 origin to those of the lowest ; in other words, to consist indi- 

 vidually of the cell-granules. In the more simply-constructed 

 of the filamentous or hair-like species, propagation takes place 

 by the effusion of these granules, the cells which contain them 

 being ruptured indiscriminately by their enlargement. In 

 others of more advanced and complicated character, the ter- 

 minal cell only of the filament or of its branches dilates and 

 assumes the office, and with it the appearance of a fruit or 

 seed case ; while in other instances similar cells ate developed 

 in the axils of the branches for the express fulfilment of this 

 function, the varied modificationa of which it ia here unneces'- 

 sary to pursue. 



Some of the algse float loosely iu the water, but by far the 

 greater number of the species grow attached to rocks, stones, 

 and other substances ; sometimes simply and precariously 

 adhering by the first formed cell, more frequently by the ex- 

 tension of their bases into a plane or concave surface ; or 



