TISSUES. 3 



thin, sometimes become very thick (as seen at a fig. 1.) ; 

 this arises from a superposition of layer upon layer, 

 always within the one first formed ; by this continued 

 superposition, the vacuity of the cellule is known to 

 become obliterated. 



9. The membrane forming the walls of cellular tissue, 

 is sometimes marked with a number of circular or 

 oblong spots ; these were once supposed to be pores, 

 but are now looked upon as thinings merely of the 

 membrane in certain places ; there is undoubtedly a de- 

 privation of the substance of its texture, but no com- 

 plete solution of continuity. (Fig. 1. 6.) 



10. The general laws regarding the development of 

 this form of tissue are not yet settled, though the ra- 

 pidity of its increase is known to be considerable ; Dr. 

 Lindley calculating that the cellules of a Bovista were 

 increased at the ratio of nearly 4,000,000,000 per hour. 



1 1 . Many other shapes of cellules besides the hexa- 

 gonal, are described in books, but most of them are 

 the result of pressure upon more aboriginal forms, and 

 are no evidences of any peculiarity as regards original 

 structure. The normal types of the cellule are the 

 spheroidal and thread-like. 



12. Fibrous cellular tissue is that form of structure in 

 which fibre, in various states 



of arrangement and direction, 

 is combined along with true 

 membrane to produce a form- 

 ation distinctly cellular. This 

 structure is evident in certain 

 tropical Orchideous plants,and 

 in different parts of the organs of fructification of many 

 other individuals. 



Fibrous Tissue. 



13. Fibrous tissue, or woody fibrs, are terms adopted, 

 perhaps, more for the sake of convenience, than from 

 our being able to limit to them particular forms of 



