220 ANATOMY AND PHYSIOLOGY OF PLANTS. 



Mirbel likewise relate*, that the pores are surrounded with 

 oorders ; and that the perforations are few, and scattered in the true 

 hexagonal cells, but numerous and arranged transversely in regular 

 series in the longitudinal. 



8. In succulent and many other plants, according to 

 Mirbel's theory, the cellular substance consists of two 

 parts ; viz. cells, and the fluid contained therein : the 

 former he terms the herbaceous tissue, and the latter he 

 has denominated parenchyma ; but if we are to consider 

 the cellular integumeut as a simple solid component of 

 the vegetable organization, we must pronounce such a 

 distinction inadmissible. 



In viewing the cellular substance as the pulp or chief mass of 

 many plants, we may then very properly divide it into the cells or 

 herbaceous tissue, and into a fluid or parenchymatous material ; 

 using the term parenchyma as expressive of something intermediate 

 of a solid and fluid. 



9. We are not yet satisfactorily convinced of the 

 true nature of the cellular membrane, but of this we are 

 well acquainted, it enters, in one form or another, into 

 the composition of almost every vegetable organ. 



The roots, the stem, the leaves, and every part of the plant, even 

 the pollen itself, are formed of this cellular texture, filled with differ- 

 ent juices, according to the intention and economy of the part. 



VASCULAR SYSTEM. 



10. The vascular system consists of numerous hollow 

 tubes of different forms and structure, which are des- 

 tined either to convey the circulating juices from one 



