xvi INTRODUCTION 



of woody plants, as in the beech, birch, elm, palm and willow families. 

 Others, such as the rose and pea families, contain a large number of 

 trees and shrubs, while many, such as grasses, orchids, mustards, 

 pinks, primroses, etc., contain only an occasional woody genus or are 

 entirely herbaceous. 



Families with the simplest flowers, that is, those with the flowers 

 least changed from the fruiting organs of the ferns, are placed at the 

 bottom of the chart. Such families are found in the gymnosperms 

 and in the buttercup order. The flowers of the former are wind- 

 pollinated, and lack both calyx and corolla. The flowers of most 

 buttercups, on the other hand, are pollinated by insects, and possess 

 both calyx and corolla, or a showy calyx. These are regarded as the 

 primitive or earliest type of flower of the angiosperms. From the 

 specialization of these, in response to insect and wind pollination, have 

 been derived the orders and families of the three lines of evolution 

 shown in the chart. In detail, the primitive flower shows a large 

 number of separate stamens and separate pistils, the petals are alike 

 and separate, and there is no union between any of the four parts, 

 sepals, petals, stamens and pistils. In the increasing adaptation of a 

 flower to its work of pollination and seed production, this primitive 

 form has given rise to the higher or more specialized forms char- 

 acteristic of the various orders of the chart. The chief steps by which 

 this has been brought about are only four, namely, reduction in num- 

 ber of parts, union, change in shape, and change in position of the 

 corolla, or elevation, but these changes have not appeared in the same 

 sequence in all three lines. Reduction in number to a flower plan of 

 3, 4 or 5 has been almost universal in the groups just above the butter- 

 cups, though flowers occasionally occur with number plans of 6, y, 

 8 and even 9. In flower structure, the arrowheads are essentially 

 buttercups with parts in threes, while the lilies are arrowheads with 

 the stamens and pistils reduced in number, and the latter united to 

 form a compound pistil. In the irises, the colored perianth of sepals 

 and petals is upon or above the ovary, and in the orchids, the corolla 

 is strikingly irregular, one petal usually taking the form of a lip or 

 sack. 



In the roses, the buttercup type is modified by the gradual grow- 

 ing together of the calyx and receptacle, and finally of the ovary also, 

 with the result that the corolla and stamens are above the calyx and 

 ovary. In the lower roses, the number of stamens and usually of 

 pistils also, is large, and the pistils are separate. In the higher fam- 

 ilies, the pistils are united into a compound pistil. In the madders and 



