572 STRUCTURE AND LIFE HISTORIES 



Table V. — Sequence of Plant Gkoups, Based on the 

 Morphology of Living Forms 



Thallophytes j Algse — having chlorophyll, 



(no archegonia) \ Fungi — no chlorophyll. 



I Bryophytes — no vascular system. 

 Archegoniates J Pteridophytes ] 



(archegonia, but no seeds) 1 Calamophytes \ vascular system. 

 ( Lepidophytes J 



I Gymnosperms — no closed ovary. 

 Spermatophytes j AngiospermS — closed ovary (pistil), 



(seeds) 1 Monocotyledons — one seed-leaf. 



[ Dicotyledons — two seed-leaves. 



pteridophytes from bryophytes — hypotheses which, from 

 other trustworthy evidence, as stated above, now seem 

 untenable. 



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. 



494. Evidence from Life Histories. — In the study of 

 the life history (ontogeny) of any higher sporophyte, 

 we find that vegetative (sterile) tissues develop first. 

 On the basis of this fact it has been inferred that all repro- 

 ductive organs (stamens, carpels, sporophylls) arose by 

 a modification of vegetative organs. Other facts, how- 

 ever, lead to the directly opposite conclusion. 



495. Evidence from Comparative Ontogeny. — In 

 Chapters XVI and XXIII attention is called to the 



