DEVELOPMENT OF PLANTS 



467 



step in advance must be to the epigynous flower. This is seen 

 to be the case with the madder order, Rubiales. Here the 

 flowers are epigynous and the parts are generally in fives though 

 the carpels vary greatly in number. The simplicity in the struc- 

 ture of the flower and often also the form of the inflorescence, 

 as in the elderberry (Sambucus), bedstraw (Galium) and arrow- 



FiG. 335. Simpler forms of the Rubiales: A, inflorescence of the arrow- 

 wood (Viburnum). B, simple, epigynous flower of the elderberry (Sam- 

 hucus) — 0, ovary. C, the twin flower (Linnaea). 



wood (Viburnum) is strikingly suggestive of the LTmbellales 

 (Figs. 335, A, B; 324). It appears that each step in advance 

 is attained in a very simple way and that only gradually are 

 alterations made that lead up to the specialized types. Look 

 back over the preceding groups and orders and note that many 

 of the irregular types of flowers are preceded by a long series 

 of regular forms. So in the madder order, this new departure 

 of the flower is attended with such a simplicity of structure as 

 to render difficult the separation of some of the genera from the 

 open flowers of the Umbellales which have also arrived at the 

 same stage of development, page 450. This would not necessarily 

 imply a relationship, since it repeatedly happens both among 



