234 



THE AMEBIC AX NATURALIST 



[Vol. XLVI 



far back into the past, present a very striking illustra- 

 tion of the biological law of recapitulation. Other fea- 

 tures of the seedling might have been considered with the 

 same result. 



But ancestral conditions are not in plants confined to 

 the young individual. We find them also illustrated in 

 connection with the principles of retention and reversion. 

 The law of retention is well exemplified by the root, cone 

 and first vegetative annual ring of the Araucariineae, 

 where the Mesozoic features of structure appear only 

 less completely than they do in the seedling. The law 

 of reversion is likewise illustrated readily in this tribe 

 of conifers in connection with injuries, for the wood 

 formed subsequently to wounds shows Mesozoic charac- 

 ters, which are not a feature of normal structure. 



It appears clear from the illustration which I have 

 chosen, only one among many possible ones from the re- 

 sults of recent coordinated anatomical, developmental, 

 experimental and paleobotanical investigations, that we 

 have definite laws of plant evolution. It is further clear 

 that like Ulysses we must "follow knowledge like a sink- 

 ing star" into the night of the past, if we are to reach 

 durable general biological principles. The laws of re- 

 capitulation, retention and reversion, founded on cases 

 where it is possible to trace an unbroken sequence of 

 forms, are likewise applicable to the elucidation of con- 

 ditions in groups the past of which is as yet insufficiently 

 known. A very notable example of this kind is pre- 

 sented by the Angiosperms. Here more than anywhere 

 else among the higher plants philosophical views in re- 

 gard to evolution prevail. You are doubtless all famil- 

 iar with the generally accepted dictum, forming a feature 

 of all elementary botanical instruction, that the woody 

 stem of perennial Dicotyledones is derived from one of 

 herbaceous texture. This conclusion is based on the old 

 fallacy, that simpler conditions are necessarily antece- 

 dent to more complex ones and antedate them in time. 

 If we investigate the primitive type of stem organization 



