138 



HEREDITY AND EVOLUTION IN PLANTS 



i 



Uj 



FILICALCON STOCK 



ANCESTRAL 



TICAL) 



FIG. 69. Hypothetical genealogical tree to illustrate the probable 

 affinities of the modern plant orders. This diagram is intended to indicate 

 that the plant orders now existing are the tips, only, of the branches of a 

 genealogical tree, whose lower limbs and roots extend into preceding geo- 

 logical periods. Our knowledge is not sufficient to enable us to connect 

 these branches with each other, nor with the main trunk. The diagram 

 teaches that hypothetical (indicated by the dotted line) Anthocerotales 

 gave rise to a now fossil Filicalean stock, from which have been derived all 

 the modern orders above the mosses and liverworts. 



