VEGETABLE ANATOMY. 201 



of the cells and tubes ; you are next to observe their 

 sides ; or otherwise you will not distinguish between 

 tubes and cells. To besfin ao^ain with the bark. You 

 will now find that the cause of the different appear- 

 ances in the two layers of the bark is owing to the 

 outer layer (B.yi — g.) consisting of round cells, while 

 the inner consists of long cells (B. e. — -f.), whose prin- 

 cipal diameter is parallel with the stem ; of these two 

 layers, the outer is purely parenchymatous, and ana- 

 logous to the cortical integument, the inner is partly 

 woody and analogous to the liber or inner bark of other 

 Exogens. You will next see that the spiral stratum 

 (B. d. — e.), is composed exclusively of thin roundish 

 cells, and spiral vessels of the largest size ; that the 

 compact, homogeneous outside (B. c. — d.) is ex- 

 clusively composed of woody tubes ; that the wood 

 itself (B. b. — c.) consists externally of woody tubes, 

 which gradually, as they approach the pith, acquire 

 an hexagonal form ; and that in addition to the small 

 spiral vessels lying amongst them, are some jointed, 

 dotted tubes, which were not before distinguished ; 

 finally, that the pith is really composed of nothing 

 but large, round polygons, mixed with great spiral 

 vessels, as at first appeared. 



You must not suppose that, because the Nepenthes 

 is an Exogenous plant, therefore all other Exogens 

 have exactly this structure. On the contrary. Nepen- 

 thes is one of the greatest anomalies I am acquainted 

 with, and stands quite alone, so far as observation has 

 yet gone, in several parts of its anatomy. For in- 

 stance, no other known plant has spiral vessels 



