CONIFERALES 



335 



testimony, not only from American, but also from European de- 

 posits, is strikingly distinguished by the fact that it produces 

 both horizontal and vertical resin canals resulting from injury 

 (Fig. 243). This condition is in contrast to that manifested by the 

 other genera of the Abieteae, in which only vertical resin canals 

 make their appearance in the secondary wood after wounding. It 

 is now generally admitted by competent anatomists that there is 

 strong evidence for the 

 derivation of the Abieteae 

 from the Pineae as a re- 

 sult of reductionary 

 modification. This con- 

 clusion is reached, not 

 only on the testimony 

 supplied by the resin 

 canals as described above, 

 but also from the com- 

 parative anatomical 

 consideration of the 

 organization of the rays 

 and the parenchyma of 



FIG. 243. Transverse section of the wood of 

 Cedrits deodara formed after injury, showing 

 reversionary appearance of resin canals in both 

 vertical and horizontal planes. 



the secondary wood. It 

 is apparent in regard to 

 these particular struc- 

 tures that the Pineae are 

 more primitive than are the Abieteae. The ray of the Abieteae 

 is often characterized by the loss of the marginal tracheids so dis- 

 tinctively developed in the radial parenchymatous strands of 

 Pinus and its living allies. 



The internal conditions in the Pineae may now claim our 

 attention. Here we find a striking separation between Pinus on 

 the one hand and Picea, Larix, and Pseudotsuga on the other, 

 resulting from a consideration of the lining of the resin canals 

 in the wood. In the first-named genus the secretory canals are 

 lined by thin- walled parenchyma which, in the transformation 

 of heartwood into sap wood, develops processes known as tyloses, 

 which more or less completely occlude the resin canals. In the 



