LESSONS IN OEOLOOY. 



118 



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LESSONS IN GEOLOGY. XL 



THE VEGKTAltl.K .CINODOM CLA88IFICATK >N >!' ROCKS. 



FOSSIL botany H in a very unsatisfactory state, therefore wo 

 Hhall not describe the vegetable kingdom HO fully OH we have 

 that of the animals. 



lining the structure of all vegetable organisms, we shall at 

 . . i>l'- them into CELLULAR and VASCULAR that is to say, 

 in one class wo shall not be able to discern uny regular forma- 

 tion ; but the substance of the plant appears to be made up of 

 fibres interlaced, without any definite order. This peculiar 

 growth may bo seen in Fungi (mushrooms, etc.) or in Algae 

 (sea-weeds), and is considered the lowest development of vege- 

 table lit".'. 



The Vascular plants exhibit a more complex structure. They 

 contain vessels, through which sap the blood of the vegetable | 

 world circulates, by means of which the plant grows, Cowers, i 

 and fructifies. 



The manner in which 

 I'lunta are propagated 

 affords another means 

 of classification. 



Many of the cellular 

 plants have no seed- 

 organs, but they seem 

 to be produced from 

 sprouts, which shoot off 

 from the mother plant ; 

 from this peculiarity 

 they are called Thalo- 

 gens. 



The vascular plants 

 bear a division both as 

 to their seeds and the 

 manner of their growthi 



1. The Cryptogams 

 do not show any seed- 

 organs, nor yet perfect 

 flowers. Ferns belong 

 to this family ; the 

 spore or seed of which 

 appears attached to the 

 under-snrface of the 

 fronds. Mosses, equi- 

 setums, mare's-tails, 

 etc., are all cryptogams; 

 and many fossil plants, 

 we shall find, belong to 

 this group. 



2. Phanerogamic mo- 

 nocotyledons, or " flower- 

 ing plants with one 

 seed-lobe " grasses, 

 lilies, palms, canes are 



this family. 



3. Phanerogamic gymnosperms. Flowering plants, but having 

 naked seeds. The very widely-distributed tribe of the Conifera, 

 or firs, belongs to this family. 



4. Phanerogamic dicotyledons. Flowering plants having two 

 .-lobes. This is by far the largest class, and comprehends 



all true forest trees and shrubs. 



The division as to their manner of growth is interesting. The 

 cryptogams increase at the point only, which is pushed further 



id further, elongating the leaf. This is readily observed in 



e mosses and the ferns, which latter unroll the leaf or frond 

 ly formed from the root. From this " point-growth " they 

 termed Acrogens. 



The next class, the Phanerogamic monocotyledons, grow in a 

 peculiar way, which is well illustrated in the cane and 

 bamboo. They shoot out from the knots or joints ; not a thin 

 twig, which gradually increases in size, but a thick, succulent 

 piece, which hardens, but does not increase. Thus they are said 

 to " grow from within," and are termed Endogens. The struc- 

 ture exhibited by a section of sugar-cane illustrates the appear- 

 ance of the " wood ; " it is full of minute holes, with no marks 

 of grain. 



The Phanerogamic gymnosperms are a connecting link be- 

 tween the endogens and the exogena. The wood of the pine 



86 N.F 



or fir-tree, if examined under the microscope, u readily distin- 

 guiithod from the true wood of the exogen* bj the pretence of 

 minute dotted vessels. 



Tho Pkanero<jamic dicotyledon* are exoyent that U, the up 

 rises up the interior of the tree, and, reaching the extremity of 

 the branches, it descends bj the bark, and pnta on every year 

 another layer of wood. The tree thus "grows from the outside," 

 so that, when a section of a tree is made, the number of rings 

 counted from the outside to the centre indicate* the age of the 

 tree. 



The above classes are subdivided into orders, which contain 

 about 300 genera and 100,000 species. 



Remembering that the fossiliferous rocks are of aqueous 

 origin, it will readily be expected that the great majority of 

 fossil remains must be of aquatic animals and plants, chiefly, 

 however, marine. 



Any land animal or plant which is found in a fossil state mas* 



have been embedded by 

 accident. For instance, 

 a flooded river carries 

 down to the sea the 

 bodies of animals sur- 

 prised by the rising 

 waters, and also plants, 

 which are torn up by 

 the impetuosity of the 

 swollen current; but, 

 in comparison to the 

 number of aquatic ani- 

 mals and plants which 

 exist in the water, and 

 when they die become 

 embedded in the sedi- 

 ment, the number of 

 land organisms must 

 be very small. Still 

 fewer remains of birds 

 Day we expect to find ; 

 and those which would 

 be most likely to be pre- 

 served in the accumu- 

 lating strata would be 

 birds which inhabited 

 the sea-shores, or the 

 banks of rivers or 

 marshes. 



When we bear in mind 

 the almost insignificant 

 scratchings of geolo- 

 gists in the rocky sur- 

 face of the earth what 

 a very small portion of 

 the crust has been exa- 

 mined we cannot but 

 wonder at the very 



numerous list of fossils which have been collected, and be led to 

 think what vast records of animal and vegetable life the rocks 

 could unfold had we power to examine the strata fully. To give 

 the reader some idea of the number of fossils, and the relation 

 the past bears to the present orders of life, we transcribe a list 

 of British fossils, compiled by Professor Jukes. Since the table 

 was constructed, some of the numbers have altered ; bat it is 

 sufficiently accurate for our purpose. 



LIVING AND FOSSIL SPECIES IK THE BRITISH ISLANDS. 



FOREST OF THK CARBONIFEROUS PERIOD, SHOWING GIOANTIC TRBE 

 FERNS, ETC. 



" Testneea " is a 

 " shielded " by shells. 



rord usually applied to all molluscs which ar 



