postelsia 61 



of certain grasses represents a second 

 vestigial cotyledon, thus indicating a 

 dicotyledonous origin for this family. 

 Nageli, however, departed from the 

 universal view when he said : * ' Der 

 Embryo der Gefasskryptogamen u n d 

 der Phanerogamen ist kein Caulom, 

 sondern ein Thallom, wie das Moosspor- 

 angium, aus dem er phylogenetisch her- 

 vorgegangen ist; die Samenlappen sind 

 keine Phyllome, sondern Thallomlappen. 

 An dem Embryo tritt als neue Bildung 

 der Stengel auf." He implies that in 

 its ontogeny the plant recapitulates its 

 phylogeny, that as an embryo it is 

 simply in an undifferentiated 'thallom' 

 condition comparable to the moss spo- 

 rophyte from which it was phylogenet- 

 ically derived, and that the stem, phylo- 

 genetically of more recent origin, later 

 arose as a new structure through the 

 differentiation of the thallome. But 



