130 HEREDITY AND EVOLUTION IN PLANTS 



arrangement of plant groups as representing the general 

 course of their evolution (Table I) : 



From what has already been said, however, it should 

 be understood that such a table represents, not the line 

 of evolutionary advance, but the paths travelled by plants 

 in the course of their development. For example, it im- 

 plies that dicotyledons were derived from monocotyledons, 

 pteridophytes from bryophytes hypotheses which, from 

 other trustworthy evidence, as stated above, now seem 

 untenable. 



TABLE I . SEQUENCE OF PLANT GROUPS, BASED ON THE 

 MORPHOLOGY OF LIVING FORMS 



Thallophytes f Algae having chlorophyll, 



(no archegonia) \ Fungi no chlorophyll. 



f Bryophytes no vascular system. 

 Archegoniates J Pteridophytes ) 



(archegonia, but no seeds) | Calamophytes \ vascular system. 

 Lepidophytes J 



Spermatophytes 

 (seeds) 



Gymnosperms no closed ovary. 

 Angiosperms closed ovary (pistil). 



Monocotyledons one-seed leaf. 



Dicotyledons two-seed leaves. 



Again, the table suggests that Angiosperms were de- 

 rived from Gymnosperms, and therefore appeared late 

 in the history of plant life; but the study of fossil plants 

 shows that they appeared in the geological past, and were 

 dominant in the Tertiary period, as now, We are led, 

 therefore to proceed with caution in drawing inferences 

 based only upon a comparative study of the structure of 

 forms now living. 



104. Consequences of an Amphibious Habit of Life. 

 The life history of the fern affords a concrete illustration 



