550 



CONSERVATIVE ORGANS. [LECT. X. 



considerable heights, as in the more perfect 

 plants, the conducting tube is consequently more 

 simple. If, however, we take a plant in which 

 the vessels convey a colourless fluid through a 

 coloured cellular structure, as, for example, Mar- 

 chantia polymorpha, we find that the surface of the 

 lobes of the leaf-like frond, when examined by an 

 ordinary lens, is reticulated by depressed lines, 

 within each of which a small nipple-like body rises. 

 When a thin slice (1. c.) of a lobe is placed under 

 the microscope, these lines are discovered to be 

 occasioned by vessels which run immediately 

 under the cuticle, anastomosing with one another, 

 as represented at 1. d. d. d. d.; and the papillary 



bodies are seen to be cuticular pores surrounded 

 by a slight elevation of the cuticle (1. b. b.) 

 modified as shall be afterwards described. This 

 vascular network is formed by a single porous 

 tube, branching and anastomosing so as to form 

 irregular, lozenge-shaped meshes, which are 

 filled with a dark-green cellular parenchyma. 



