294 FLOWERS 



It is evident that a flower may be primitive as to 

 some whorls and advanced as to others. In other char- 

 acteristics, as well as in this one of the numbers of the 

 parts, flowers often show a mixture of primitive and ad- 

 vanced features. Thus, actinomorphic flowers are some- 

 times epigynous, as in wild parsnip, while zygomorphic 

 flowers are often hj^ogynous, as in snapdragon or members 

 of the mint family. Thus you can see that it is impossible 

 to arrange flowers in a series from the most primitive up 

 to the most advanced. Evolution has evidently proceeded 

 by many branching roads rather than along one main high- 

 way. Also it is not necessarily true that the simplest 

 flowers are the most primitive or that the most complex 

 flowers are the most advanced, for evolution may result in 

 an increase in simplicity as well as in an increase in com- 

 plexity. Thus flowers of the dandehon type, though ap- 

 parently quite simple, are believed to be the most advanced 

 type of all. (See Figure ii6.) 



Three and five appear to be the favorite floral numbers. 

 That is, when the parts do occur in definite numbers it is 

 usual to find three or five of each kind of part, except that 

 stamens are quite commonly just double the number of 

 the other parts. You have noted this in the case of the 

 Hly. 



G. Monocotyledons and Dicotyledons. — Three is the floral 

 number which is characteristic of the monocotyledons, and 

 five is the floral number which is characteristic of dicotyle- 

 dons. (See page 183.) This may be noted in the examples 

 given above among which the lily is the only monocotyle- 

 don; the others are all dicotyledons. This rule as to 

 floral numbers is by no means invariable. In some families 



