LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 437 



cells, which appear symmetrically arranged in the 

 longitudinal section of the root: the second, those 

 which consist of sap and proper vessels, and com- 

 mon cellular matter only, exhibiting no peculiar 

 symmetry of arrangement in the longitudinal sec- 

 tion. 



1. Perennial herbaceous roots composed 

 chiefly of tubular cells symmetrically arranged. 

 As examples of this class, we may select the roots 

 of Dandelion and of Marsh Mallow; because the 

 principal secretion in the one is an opaque, white, 

 glutinous fluid, and that in the other a transparent 

 colourless mucus. 



If we place a transverse and a longitudinal slice 

 of the root of Dandelion, Leontodon Taraxacum, in 

 the first year of its growth, un- 

 der the microscope, it appears 

 composed of a cellular pith a. 

 (see marginal cut), surrounded 



by ten fasciculi of sap vessels 

 b. ; and a very thick cortex, 

 which consists, interiorly, of a 

 concentric layer of smaller cells 

 arranged in rays, through which run numerous 

 fasciculi of proper vessels, c. arranged so as to 

 form three concentric circles ; and exteriorly of a 

 mass of hexagonal cells, the same as the pith 

 covered with a thick cuticle, d. The sap vessels are 

 punctuated, the perforations being oblong trans- 



FF3 



