TAXONOMY 



309 



Stems, and roots of secondary growth with open collateral fibro- 

 vascular bundles, radially arranged about pith. 

 Exogenous stems. > -, ' : 



Medullary rays present. 

 Cambium. 



PIG. 172. Morphology of a typical dicotyledonous plant. A, leaf, pinnately- 

 netted veined; B, portion of stem, showing concentric layers of wood; C, ground- 

 plan of flower (the parts in 5's); D, perspective of flower; E, longitudinal section 

 of seed, showing dicotyledonous embryo. (Gager.) 



Roots developing secondary structure. 



Flowers tetra- or pentamerous (parts of each whorl, four or five or 

 multiple thereof). 



SUB-CLASS A. ARCHICHLAMYDE^E 



Those dicotyledonous plants in which the petals are distinct and 

 separate from one another or are entirely wanting. That group of 



