78 Elkins and Wieland — On Devonian Wood. 



figures and the attention they invite to one of the best con- 

 served Devonian woods ever sectioned. Doubtless some de- 

 tails of structure have been imperfectly observed or under- 

 stood by us, but the results show an advanced structural type 

 which can stand in an ancestral relationship to other gymno- 

 sperms, or even be regarded as standing near to cycadaceous 

 types, and slightly in advance of the actual line leading into 

 the modern Araucarians. Moreover this wood suggests that 

 it may well be that both Jeffrey and Thomson are virtually 

 correct when the one assigns a high antiquity to Araucarian, 

 and the other equal great age to Abietineous structures. The 

 fact that the latter have undergone much variation in Creta- 

 ceous time, playing the great role in the Cretaceous coniferous 

 forests, merely makes the ancestral Abietineous features harder 

 to discern ; whereas in the Araucarians primitive structures 

 stand out in bold relief. At least it is evident that great 

 variety of structure exists in Devonian woods, and consider- 

 ing the further diversity of the ancient seed types it begins 

 to appear that if there is any past period which can be 

 fairly singled out as the true age of gy mnosperms it must be 

 Devonian time. 



Eandolph-Macon Woman's College. 

 Yale University Museum. 



EXPLANATION OF PLATES. 



Plate I. 



Photomicrograph 1 (above). Radial section of wood showing the radially 

 grouped pits and the highly characteristic appearance produced by these 

 together with the thickening of tracheidal walls and constriction between 

 the pit groups, x 100. Yale Museum Section No. 421. 



Photomicrograph 2 (below). Transverse section of wood interior to growth 

 ring, showing marked variation from large rounded to pentagonal rhom- 

 boidal and other outlines. See fig. 2. Yale Museum Section No, 420. 



Plate II. 



Photomicrograph 3 (above). Tangential section of wood, x 100. Yale 

 Museum Section No. 427. 



Photomicrograph 4 (below). Eadial section of wood, x 280. Focussed 

 to bring out the a?-figure formed by the crossed slits of paired pits of 

 appressed tracheids. [Neither slit is in full focus in such a photograph.] 

 Yale Museum Section No. 421. 



