304 ESSENTIALS OF BOTANY 



the lower ones, he would probably put some one of the 

 green algse at the bottom and the angiosperms at the top 

 of the series. 



385. The Oldest Angiosperms. — It is impossible to give 

 any of the reasons for the statements of this section with- 

 out making an unduly long chapter. It is not yet certain 

 whether monocotyledons or dicotyledons were the first to 

 appear on the earth. The descent and various relation- 

 ships of the families of dicotyledons can be discovered by 

 the study of the flower, fruit, and seed better than by the 

 examination of the vegetative organs. 



The entire pedigree of the several families cannot be 

 represented by arranging the names of the families in a 

 straight, line. Their relationships can be shown, however, 

 in a general way, and a part of the pedigree is indicated 

 by the succession of families in the Flora which accom- 

 panies this book. The Willow family is perhaps the oldest 

 of the more familiar families of dicotyledons, and the Com- 

 posite family the youngest. The beginner must remember 

 that it is not such " typical " flowers as are shown in 

 Figs. 97 and 98, but rather bilaterally symmetrical ones 

 like Fig. 101, or epigynous and closely grouped flowers like 

 those of the Composite family (Appendix I, Fig. 8), that 

 represent the highest development among flowers. 



386. Division of Labor and Plant Evolution. — A little 

 has been said in Sect. 384 about the steps of development 

 in the reproductive processes of plants. In general the 

 more complicated kinds of reproduction are found among 

 the younger and higher types of plants. The same gen- 

 eral law applies to the vegetative parts of the plant body. 



The lowest undoubted plants (Figs. 150, 169) show very 

 little division of labor among their parts. A single cell 



