No. 448.] 



NORTH AMERICAN CONJFE RALES. 



^S7 



species of this genus which have been critically studied within 

 recent years (39) there is a general agreement in the constancy 

 of this character which thereby becomes of generic value. In 

 all the species the pits are disposed in such a compact manner 

 throughout the entire extent of the tracheid, as to present a hex- 

 agonal outhne. In Cordaites acadianuin, they are 2-5-scriate 

 (Fig. 5). In other species they vary from 2-seriatc in C. Iiamil- 

 toncnse and C. neivbcrryi (Fig. 6) to occasionally 4-scriate in C. 

 clarkei. In the majority of species, the rows arc not constant, 

 but show a varying number from i to 3, or 2 to 5. this variation 



bemg exhibited by adiacent trachcids m 

 variation ot the latter m ladial diamctei 

 tnbution as a whole, it cannot be doubt 

 corresponding differences iir development 

 striking features of the genus is to be mel 

 (Fig. 6), which IS unique in the segregation 

 of 6-13. 



In Araucarioxylon Knowlton has shov 

 while conforming to the characteristic torm 

 ment presented 



614) that, 

 ict arrange- 



their serial 



ent. and in this rcsi)ect they 



