508 



PART III. THE CLASSIFICATION OF PLANTS. 



A B 



FIG. 322. A Diagram of the pentamerons flower 

 of Primu'a, showing the five planes of symmetry; 

 the stamens are antipetalous ; there are no pro- 

 phylla. B Diagram of the tdmerous flower of 

 Lilium, showing the three planes of symmetry. 

 (After Eichler.) 



by the section in six of the planes are unlike those produced by 

 section in the other six planes. 



The symmetry may be isobilateral ; in this case the flower is 

 divisible into symmetrical halves in two planes, but the halves 



produced by section in one 

 plane are unlike those pro- 

 duced by section in the 

 other plane. Thus, a re- 

 gular eucyclic dimerous 

 flower (e.g. Circcea luteti- 

 ana, Fig. 323 B ; Fraxinus 

 dipetala\ is symmetrically 

 divisible in the median 

 and lateral planes, but the 

 halves produced by the 

 median section differ from 

 those produced by the 

 lateral section. This is 

 true also of some regular 

 heterocyclic flowers, such as those of the Cruciferae, Jasminum, 

 Olea europcea, Cornus, Hamamelis, the whorls of which are 2- 

 or 4- merous, and of the somewhat peculiar flower of Dicentra. 



The symmetry may be zygomorphic, that is, the flower may be 

 mow asymmetrical, there being only one plane in which it is sym- 

 metrically divisible. This condition is to be found in regular 



heterocyclic flowers, and 

 is the result of oligomery 

 of the whorls, generally of 

 the gynseceum, rarely of 

 the androecium. Flowers 

 of this type are common 

 among Dicotyledons (e.g. 

 in the Ribesiaceae, Apo- 

 cynaceas, Boraginacece, 

 Solanacea3, Gentiariaceae, 

 Campanulaceee, Compo- 

 sitae, Rosaceae, Saxifrag- 

 aceas, Umbelliferee, etc), 



FIG. 323 A Diagram of the tetramerons flower 

 of Fuchsia, showing the four planes of symmetry. 

 B Diagram of the dimerous flower of Circsea, show- 

 ing isobilateral symmetry. 



the oligomerous gynasceum having 1-4, generally 2, carpels, the 

 rest of the flower being pentamerous or hexamerous. In this case 

 the plane of symmetry is determined by the position of the carpels. 



