ANATOMICAL CHARACTERS IN THE EVOLU- 

 TION OF PINUS 1 



IRVING W. BAILEY 

 Harvard University 



Pinus is jthe oldest genus of the conifers and the most 

 important and interesting, whether considered from the 

 botanical, economic or aboricultural standpoint. Occur- 

 ring as it does in many species throughout the whole 

 northern hemisphere, from it are derived many of the 

 most valuable timbers and extractable products of com- 

 merce. In accordance with the general impression, that 

 llouri-liinir m-ncra arc ni< •< Icrn. -'nice tlicy -how an obvi- 

 ous adaptation to existing conditions of environment, it 

 has been assumed that Pinus is of comparatively recent 

 origin and marks the last word as it were in coniferous 

 development. Recent investigations however of the oc- 

 currence of Pinus in the American Cretaceous, show that 

 in the lower levels of that epoch, species of pines were 

 apparently much more numerous than they are at the 

 present time. It is accordingly apparent that so an- 

 cient a genus as Pinus and one so richly endowed with 

 an abundant modern progeny supplies a particularly 

 favorable subject for evolutionary investigation. 



It has been the practice in the past to arrange plants 

 systematically on the basis of external characters alone, 

 chiefly on the superficial features of their floral organs 

 and leaves. In the case of so ancient a genus as that 

 under consideration, this procedure has peculiar diffi- 

 culties connected with it, since in the tremendous period 

 of time during which it has been in existence, its exter- 

 nal characters have undergone many puzzling changes. 

 The internal structure of the genus however has shown 



i Contributions from the Phanerogamic Laboratories of Harvard L T ni- 

 284 



