174 



Plant Life and Evolution 



from response to similar conditions in independent 

 developmental lines (Fig. 19). This would seem to 

 be an excellent illustration of determinate variation 



FIG. 19 



Parallelism in the evolution of the flower in Monocotyledons 

 (upper row) and Dicotyledons (lower row). 



A Apetalous flower of a Sedge (Carex). 



B Apetalous flower of a Mulberry (Morus). 



C Apocarpous flower of Water-plantain (Alisma). 



D Apocarpous flower of Rue- Anemone (Thalictrum). 



E Zygomorphic sympetalous flower of an Orchid 

 (Arethusa). 



F Zygomorphic sympetalous flower of Dead-nettle 

 (Lamium). 



(Fig. C, after Britton & Brown.) 



in several lines starting from a common stock and 

 resulting in very similar structures at the end of 

 these diverging lines of development. In both of the 

 great divisions of the angiosperms, the lower types 



