THE FLOWER 



229 



In many cases the petals are not all alike, and the radi 

 ate character, with its similar parts repeated about a cen 

 ter, is lost. In the 

 common violet, for 

 example, one of the 

 petals develops a spur 

 (Fig. 211) ; in the 

 sweet pea the petals 

 are remarkably un- 

 like, one being broad 

 and erect, two small- 

 er and drooping 

 downward, and the 

 other two much modi- 

 fied to form together 

 a boat-like structure 

 which incloses the 

 sporophylls. Such flowers are called zygomorpMc, meaning 

 *^ yoke-form," and they are often called ^^ irregular flowers." 



When zygomorphic flowers are also sympetalous the 

 corolla is often curiously shaped. A very common form 



Fig. 211. The pansy {Viola tricoloi^) : A, section 

 showing sepals {I, I'), petals (c) one of which 

 produces a spur (cs), the flower being zygomor- 

 phic; B, mature fruit (a capsule) and persistent 

 calyx (k); C, the three boat-shaped valves of 

 the fruit open, most of the seeds (s) having 

 been discharged.— After Sachs. 



Fig. 212. Flower of a mint {Mentha aquatica): A, the entire flower, showing calyx 

 of united sepals, unequal petals, stamens, and style with two stigma lobes; B. a 

 corolla split open, showing petals united and the four stamens attached to the 

 tube; the flower is sympetalous and zygomorphic— After Werminq, 

 33 



