CONIFERALES 



245 



ent in the main body of the wood. Consequently, the Araucariaceae 

 could not have come from the Cordaitales, and any theory of the 

 origin of the Coniferales would have to make the Abietaceae the 

 most primitive group. Thomson^^^ (1913) found a bar in Araucaria- 

 cean wood and believed the bars are present, in rudimentary form, 

 in all the family. 



A cytological study of the origin and development of the bordered 

 pit and the bars and rims of Sanio would be 

 interesting. The technique which has been 

 developed in studying the structure of proto- 

 plasm and chromatin could be modified, if 

 necessary, for a study of these structures. 

 Dr. Grace Barkley's^^ work on the origin 

 of spiral thickenings in the protoxylem of 

 Trichosanthes anquina was a step in solving 

 the relation of protoplasm to the spiral band. 

 Anatomists, who have the foundation for the 

 problem, lack the technique ; while cytologists, 

 who have the technique, lack the foundation 

 for such problems, and, besides, they can 

 think of nothing but chromosomes. 



In the Taxaceae the tracheids have a ter- 

 tiary thickening of the cell wall, in the form 

 of a spiral band, which looks somewhat like 

 the spiral thickening in protoxylem, except 

 that it is very commonly double. A similar 

 thickening is also found in Pseudotsuga. The 

 spiral is very conspicuous in Taxus (fig. 252), and gives the wood an 

 elasticity which has long made it popular with archers. The yew 

 was especially famous for bows before the appearance of the rifle. 

 The western Taxus brevifolia has even thicker spirals than the fa- 

 mous Taxus baccata, and archers are beginning to claim that it has 

 greater "cast." 



Tyloses are rare in conifers. Chrysler'-''' found them only in 

 Pinus, and there only in the root and in the axis of the female stro- 

 bilus. He examined the roots of 32 species in 13 genera, and cone 

 axes of 23 species in 8 genera. 



Fig. 251. — Pinus slro- 

 bus: bars and rims of 

 Sanio, showing separate 

 and fused conditions; 

 X375- 



