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52 Vegetable Organography and Physiology. 
These four primary tissues, constitute the only elementary or 
gans which enter into the structure of vegetable formations. 
There are other organs connected with the phenomena of veget- 
able life, but they are composed of some one of these elementary 
ssties. 
Of all the elementary organs which enter into the composition 
of plants, the cellular tissue is the most abundant. © It is the basis 
of all vegetable structure, and is the only tissue that is universally 
esent. ‘The other forins sometimes entirely disappear, or are 
never developed. 
The first natural division of all plants i is into two grand clacoell 
arranged according to the presence or absence of one of these pri- 
mary tissues, viz. the spiral vessels. It has been ascertained that 
all flower-bearing plants, or those which are propagated by means 
of sexual organs, have spiral vessels; whilst those vegetables 
which have no flowers are destitute of spiral vessels.* 
‘The first class is denominated vasculares ; the latter cellulares. . 
Under the head of cellular plants are included the numerous tribes 
of Ferns, Mosses, and Lichens; vegetables which, to the unini- 
tiated observer, may appear of little importance in the operations 
of nature. Yet, without their aid, many parts of our globe, which 
are now teeming with vegetation and life, must have remained 
barren and uninhabited wastes. Some of the tribes of cellulares, 
as the mosses and lichens, of which there are several thousand 
‘species, may be deemed the pioneers in vegetation. They are 
found where no other forms of vegetable life can exist. Attached 
to the bare rocks of newly found countries, and islands in the 
ocean ; springing into life on the surface of the encrusted lava, 
they vegetate and decay ; and thus, by depositing the remains of 
sticcessive generations, gradually prepare these barren surfaces 
for higher grades of vegetable life. “ How they find their way 
to such places,” says Dr. Lindley, “and under what laws they 
are created, are mysteries that human ingenuity has not succeeded 
in unveiling.” 
Both the anatomy and the physiology of vascular plants are 
better understood than the growth and functions of cellulares- 
The organs of the circulating system, also, and the course of the 
nia? in vaseulares are now very well known, whilst much doubt 
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* Introduction: to the Natural System of Botany, by J. Lindley, &c. p. 16. 
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