Nos. 45 1 -452-] ANATOMY OF THE CONIFER ALES. 



series in the order given, but rather that they represent separate, 

 though short, side hues of development, between which the 

 general sequence is manifested. 



Structural. 



Our studies of the resin cell have shoAvn how peculiar aggre- 

 gates of these structures lead in a natural way to the organiza- 

 tion of resin passages, the structure of which it is now necessary 

 to discuss somewhat in detail, and in doing so it will be most 

 profitable to have reference to (i) the primitive form, (2) the 

 intermediate form and (3) to the advanced or fully organized 

 form. 



The primitive form of the resm passage is to be found m 

 Sequoia, Tsuga, and Abies and inasmuch as within these genera 

 they exhibit differences m organization which C(.)rresi)ond ap- 

 proximately to the sequence given, it will be nece;>saiy to dibcu.ss 

 them somewhat in detail, with special reference, ho\vevei, to 

 Sequoia. This genus possesses special interest with respect to 

 the occurrence and organization ot secietor)' reseivoirs, since it 

 is in all probability not only the most ancient genus m whuli 

 such structures occur, but it is, so tar as I am await,-, the <>iil\ 

 genus affording special data with respect to impoit.iiu \cUiatinn> 



the most primitive ot the tlirec genera, I shall deal with it liist. 



In Sequoia ^mipi i . u ui^ the sceieton K-u\nii^ ikuii in 

 rows within the initial la\eis of the spimg wood, md tht \ thuie- 

 fore lie exactly on the outer tace of the sununer w<kh1 ..t the 

 previous year. Within this row the leseuoiis au ». (inti,..,u<)u.s 

 and in many cases they become conHuent so as to lonn a mon. 

 or less extended and continuous compound u:sei\oii Ixiu.^tan- 

 gentially. In their most rudimentary foim.s the) |)tesLnt the 

 aspect of simple aggregates of resin cells without aii\ ditteienti 

 ation of a resin sac or of an epithelium. In a moiL cuKaneed 

 stage of development there is produced a eeiitial (.a\ it\ m the 

 form of an intercellular space (Fig. 43» '^''^^^^^'^ ^^^^^ obMou^l) 



