DICOTYLEDONS 



207 



perianth segments are always free (Gr. choris, free; 

 petalon, a petal) — i.e., tliey are never fused together; 

 but in the Sympetalee (Gr. syn, together, and petalon) 

 a corolla is always present, as well as a whorl of sepals^ 

 and the petals are invariably united or coherent. Some- 

 times the sepals are also joined. 



In attempting to decide which of the Dicotyledons 



Fig. 66.— Compound Umbel of 

 Carrot. 



Pig. 67. — Hazel. 



(J, Male catkins; 5 , female 

 catkin. 



are lower or higher, as the case may be, it is necessary 

 to understand the principles upon which such a decision 

 rests. The fundamental principle must needs be special- 

 ization. We have already appreciated the fact that all 

 the organs of a flower are modified leaves : the sepal is a 



