OF VEGETABLE TISSUE. 11 



sessed by the cells which compose this tissue, 

 forms a very important part of the history of 

 vegetation, for it is to these adhesions in the 

 cellular tissue, that all the seams in the various 

 organs of a plant are owing. The term paren- 

 chyma is applied to the cellular tissue, consi- 

 dered as a mass, to distinguish it from those 

 parts which abound in vessels. Cellular tissue 

 " is self productive, one cell not only having the 

 power of generating another on its surface," but 

 cells frequently produce others, generally in a 

 definite number, within their own cavities, on 

 the complete development of which, the parent 

 cell generally perishes or is re-absorbed. 



3. Vessels, or Vascular Tissue. This term is 

 applied to tubes, nearly or quite cylindrical, 

 which are observed in the greater number of 

 plants. They are now usually distinguished as 

 Spiral Vessels and Ducts. 



A. Spiral Vessels,or Tracheae, resemble a rib- 

 bon which has been rolled round a cylinder, and 

 which by its spiral convolutions forms a con- 

 tinuous tube. These vessels are very apparent 

 in the young shoots of plants, particularly those 

 which can be readily broken without tearing, 

 such as the rose, &c. They are formed in the 

 medullary sheath (27) in the nervures of leaves, 



