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 

 tissues. 



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 

 present. The other forms sometimes entirely disappear, or are 

 never developed. 



The first natural division of all plants is into two grand classes, 

 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 vascular es; 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 

 successive 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 

 sap in vasculares are now very well known, whilst much doubt 



* Introduction to the Natural System of Botany, by J. Lindley, &c. p. 16. 



