54 CLASSIFICATION OF DICOTYLEDONS. [CHAP. 



and merely serve, therefore, to render the flower-head 

 more conspicuous. The calyx, moreover, is usually 

 green ; but when the position of the flower is such 

 that it is much exposed / it becomes brightly coloured, 

 as, for instance, in the Berberry or Larkspur 



The above characters, though true in the main, do 

 not hold good in all cases, For instance the genus 

 Arum, though a Monocotyledon, has reticulated 

 nerves, but its stem is endogenous, and its embryo 

 has only one cotyledon. 



The class of Dicotyledons is divisible into four sub- 

 classes, which may be thus characterised :- 



Thalamifiorcs. Petals distinct from the calyx and 

 from each other, seldom wanting. Stamens 

 usually hypogynous (i.e. attached under the 

 ovary), so that if the calyx be torn away the 

 stamens remain. 



Calyciflorcz. Petals usually distinct. Stamens 

 perigynous (i.e. attached round the ovary), or 

 epigynous (i.e. placed upon the ovary). 

 Corolliflorce or Monopetalcs. Petals united (at 



least, at the base) into a single corolla. 

 Incomplete? or Monochlamydea. Perianth or floral 

 envelope, really or apparently simple ; or none. 

 These subclasses may be tabulated as follows : 



Perianth / single or none Monochlamydese. 



or floral [ corolla of united petals . . . . Corolliflorse. 



envelope double I i i 



stamens hypo- Thalamiflora . 



I corolla of dis- ^ nous ' '$ 

 tinct petals \ ^^ perigy _ , 



nous orepigy- / Calyciflone. 

 nous . . . ) 



