262 ' THE AMERICAN NATURALIST. \yo\..XXX\\\\. 



is true of a slow rate of growth which is again convertible into 

 terms of maturity. On this basis we may present the following 

 general outline of sequence in development, as preliminary to 

 further and more detailed discussion of phylogeny. 



agonal pit 



Tangential Walls. — Th^ occurrence of bordered pits on the 

 tangential walls is a well-known and characteristic feature of the 

 Coniferales. In the case of fossil forms, to which Araucarioxylon 

 offers a partial exception, it cannot be satisfac- 

 torially demonstrated because of the peculiar 

 alterations of the cell wall, but that it is present 

 we are permitted to infer from analogy with 

 existing species upon which dependence must be 

 placed for an elucidation of the general law. 

 The typical position for such pits is upon the 

 tangential walls of the summer wood, where 

 they are most satisfactorily seen in radial sec- 

 tion, inasmuch as they are always readily obser\^- 

 able when present, and their most essential 

 features are displayed in a manner not possible 

 in a tangential section (Fig. 10). Pits occur in 

 I this position in 71.7 f of all the investigated 

 Fig .o^^^^I^ia i- ^P^^^^^' their absence in 28.3 f points to 

 gantea. Radial sec- some spcclal fcatures in development which may 

 bordere'd°JilsL ^ssumcd to havc a general bearing upon the 



tiTTummer"' q^^estiou of dcsccnt and relationship. In Agathis, 

 X 280. " ■ as represented by the one species, A. ans traits, 

 such pits are a prominent and characteristic 

 feature, but in the nearly related Araucaria, they are remarkable 

 for their uniform absence. In the primitive Ginkgoales they 



