viii INTRODUCTION 



upon the other. In the last place, it is necessary to examine the plant carefully and not merely guess 

 at the points in question. This applies also to the technical terms which cannot be avoided if 

 leaves and flowers are to be described accurately. 



In the case of a common weed, it will often be found convenient to make use of the "Key to 

 Weeds" on page xv. This is particularly true of weeds in the fall, since their flowers have often 

 disappeared. It is quite possible to place them, however, from the characters of leaves and fruits 

 by the use of the key indicated. In finding the botanical name of the sweet clover, the first choice 

 is between "1. Leaves simple," and ''2. Leaves compound." Since the leaf of the sweet clover 

 consists of three leaflets, it evidently falls under "2." The next choice is between "a. Leaves 

 with three leaflets," and "b. Leaves with more than three leaflets." The choice here falls upon "a" 

 and then the decision rests between "(1) Leaf margin entire" and "(2) Leaf margin serrate or 

 toothed." Under "(2)" the choice lies between "(a) Leaf margin coarsely serrate or toothed" and 

 ''(b) Leaf margin finely serrate." This distinction requires some experience for entire certainty, but 

 the small teeth on the leaflet of the sweet clover would seem to indicate fairly clearly that the choice 

 would fall upon "(b)." Under "(b)" the height of the plant and the arrangement of the flowers in 

 a long cluster or raceme indicate that the choice should rest upon "x. Upright plants 2-6 feet tall — 

 Melilotus alba : sweet clover," page xviii. 



EXPLANATION OF THE CHART 



The chart on page ix is designed to show the general lines of descent of flowering plants from 

 the ancestral ferns, and to indicate the relationships of the various orders. It is based primarily 

 upon the development of the flower as a special organ for pollination and seed-production. 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 characteristic 

 of the various orders of the chart. The chief steps by which this has been brought about are four, 

 namely, reduction in number of parts, union, change in shape, change in position of the corolla, or eleva- 

 tion, 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 buttercups, though 

 flowers occasionally occur with number plans of 6, 7, 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 growing 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 families, the pistils are united into a compound pistil. 

 In the madders and honeysuckles, the petals have become united, and finally, in most of the asters, 

 some or all of the flowers of the characteristic heads become irregular as to their petals. In the 

 mustards, pinks, and geraniums, the flower parts are regularly reduced to the number plan of 4 or 

 5, and the pistils are united. In the primroses, the petals become united, and in the snapdragons and 

 mints, the corolla as a rule is highly irregular. 



