3o6 MORPHOLOGY OF GYMNOSPERMS 



others; and Sinnott (162) has added another new genus from 

 Massachusetts. It was in connection with these studies that the 

 general character of this flora was outlined. One of the important 

 results was the discovery that coniferous remains which had been 

 referred to Sequoia, Cupressineae, and Podocarpineae, on account 

 of strong superficial resemblances, are really araucarians. 



Two types of wood structure have been described (155), which 

 seem to represent a phylogenetic connection of the living araucarians 

 with some very ancient type. The anatomical characters of existing 

 araucarians are summarized as follows: tracheids with radial bor- 

 dered pits alternating or flattened by mutual contact; resin canals 

 not formed as a traumatic response; medullary rays pitted only in 

 contact with tracheids; and leaves not on dwarf shoots. One of the 

 mesozoic types, including several genera whose wood has been named 

 Brachyoxylon, differs in that there is an association of araucarian and 

 abietineous pitting, the former being restricted to the ends of tracheids, 

 and also in that resin canals are formed in response to injury, as in 

 Abietineae. The other type is represented by the genus Araucariopitys 

 (127), whose tracheids show the same association of araucarian and 

 abietineous pitting, and in which traumatic resin canals are often 

 present, but whose medullary rays have pits not only on the lateral 

 walls but also on the other walls, as in Abietineae, and whose leaves 

 are probably on dwarf shoots, as in Pinus. There are thus three types 

 of araucarians, which show intergrading characters from the existing 

 type through the two mesozoic types toward the Abietineae. These 

 intergrading characters, if they have the value that has been assumed 

 for them, seem to connect in some way the Araucarineae and the 

 Abietineae, and this connection must have been a very old one. 



An abundant and world-wide araucarian flora during the Jurassic 

 and Cretaceous would at least suggest the existence of the tribe in 

 much earlier times, but the evidence from actual remains is not con- 

 vincing. The permian genus Walchia, whose leafy twigs are common, 

 some of them bearing cones, has been referred to the Araucarineae. 

 The habit is like that of some of the living araucarians; casts of the 

 pith (Tylodendron) agree closely with Araucaria, the wood is of the 

 Araucarioxylon type, and the small scaly cones suggest the same 

 connection. Even with all this agreement, however, the case is not 



