ANATOMY OF THE GYMNOSPERMS 



FIG. 36. SEQUOIA SEM- 

 PERVIRENS. Radial 

 sections showing (</) 

 the form of the resin 

 cells and the associ- 

 ated parenchyma tra- 

 cheids; (/>) resin cells 

 from the spring wood 

 showing the form of 



completely fills the entire cell cavity, but in Larix, Tsuga, and 

 Pseudotsuga it takes the form of a peripheral layer in imme- 

 diate contact with the inner face of the cell wall (plate 44). 

 The reduction thus indicated is, in some species, carried to 

 such an extent that the resin is barely recognizable, while in 



Abies it is wholly wanting. 



A relation of more than ordi- 

 nary interest is that of the resin 

 cells to certain forms 

 of tracheids. In Se- 

 quoia sempervirens it 

 commonly happens 

 that the resin cells 

 lie in immediate con- 

 tact with tracheids of 

 special form. These 

 structures are wholly 

 unlike the wood tra- 

 cheids among which 

 they are found, but 

 they are, in all essen- 

 tial respects, like the 

 tracheids of the med- 

 ullary rays. They 

 have the form of long, 

 cylindrical elements 

 with abrupt termina- 



the resin ; (c) resin cells showing transitional tioilS and they thus 

 forms with bordered pits, x 200 



bear an external re- 

 semblance in form to the wood-parenchyma cells with which 

 they are associated. They differ, however, in the distinguishing 

 presence of bordered pits upon their side and terminal walls 

 (fig. 37, a}. The relation of these two elements is nevertheless a 

 much more intimate one than is implied by mere association. 

 In Sequoia an interchangeable relation is manifested, as already 

 pointed out, in the occurrence of resin cells with bordered pits 



