130 Trans. Acad. Sci. of St. Louis. 



Closely connected with the changing conceptions as to the 

 origin and fixity of species, was a much increased interest in 

 such evidence! concerning the plants of the past as was afforded 

 by their fosiiil remains, aud, largely through the work of 

 Brongniart, Goeppert, Heer, the elder Schimper, von Ettings- 

 hausen, Saporta and Solms Laubach, and Dawson, New- 

 berry, and Lesquereux in this country, paleobotany has 

 assumed, in the last fifty years, a position of no small im- 

 portance. 



Partly because of the same reasons, the geographical dis- 

 tribution of plants and the influences controlling widespread 

 or restricted occurrence in the case of individual genera or 

 species has also assumed an importance in recent years not 

 formerly recognized for it, and on the foundation laid by 

 DeCandolle, Humboldt and Martius, Grisebach, Engler, Drude 

 and the younger Schimper have grounded a line of botanical 

 research in which morphologists, systematists and evolution- 

 ists are alike interested. 



With the change in the world's view of the fixity of species, 

 and of their several and independent origin in their present 

 form, came new and somewhat differently conceived efforts 

 to group plants in a natural system, the ultimate object being 

 virtually the production of a classification which should rep- 

 resent descent relationship as well as organic or morphological 

 affinity, and which, in a word, should present the family tree 

 of any individual group or species, — to the primitive animal 

 and vegetable main divisions of which Haeckel in particular 

 has given attention. A comparative glance at the Genera 

 Plantarum of Bentham and Hooker, the synopses of Van 

 Tieghem and Warming, and the still incomplete Pflanzen- 

 f amilien of Engler and Prantl will show how great have been 

 the changes wrought in systems of classification by the 

 introduction of these later considerations and motives. Free 

 to read heredity and atavism into the explanation of aberrant 

 minor characters, rudiments and vestiges, these men have often 

 found in the minuter details of anatomy, reproduction and 

 development most surprising indications of affinity between 

 superficially and externally dissimilar groups. That they are 

 not at one in their conclusions, indicates that the Twentieth 



