134 MANUAL OF BOTANY 



as to stand over tlie intervals between the leaves of the whorl 

 below it. As the flower is to be regarded as a modified branch 

 with verticillate phyllotaxis, its parts should be arranged upon 

 the same plan as those of the vegetative branches. The whorls 

 being four, we can devise what may be called a typical flower, 

 based upon this resemblance. Such a flower, therefore, should 

 possess a calyx, corolla, andrcecium, and gynoecium, each of 

 which should be so arranged that its parts form but a single 

 whorl ; the different whorls should consist of an equal number of 

 members ; the parts of successive whorls should alternate with 

 one another ; and the members of each should be uniform in 

 size and shape, and distinct from each other and from the 

 neighbouring whorls. This normal or typical flower is, however, 

 liable to various alterations, arising from several disturbing 

 causes, which modify and disguise one or more of its typical 

 characters. Some of these causes have been already alluded to 

 in the description of the different organs of the flower, but it 

 will be necessary for us to investigate them more fully here, and 

 classify them for systematic study. All the more important 

 deviations of the flower from the typical character may be 

 arranged under the following heads : — 



1. Irregularity of form in the members of one or more of the 

 whorls. 



2. Multiplication of parts. 



3. Suppression, or abortion of a whorl or part of a whorl. 



4. Displacement, or interference with the regular alternation 

 of the whorls. 



5. Coalescence of the parts or members of a whorl with one 

 another. 



6. Coalescence of the members of one whorl with those of 

 another. 



7. Substitution of spiral for whorled phyllotaxis. 



8. Metamorphosis of parts of the flower. 



1. Irregularity of Form — This is most commonly seen in 

 the perianth whorls. A sepal or a petal may develop a spur or 

 prolongation downwards from its base, as in the Larkspur or the 

 Indian Cress {fig. 295). If only one such structure is formed 

 the flower becomes zygomorphic. A great variety of form of 

 both calyx and corolla is caused by unequal development of this 

 kind, and it will be convenient to reserve a detailed examination 

 of the most frequently occurring cases till we discuss these whorls 

 in detail. Irregularity of this kind is also fairly common in the 

 whorls of the sporophylls. 



