8 4 



ANATOMY OF THE GYMNOSPERMS 



including fossil representatives and the Cordaitales. They vary 

 very much in form, size, and number. In such types as Junip- 

 erus they are most diminutive (fig. 23) and generally numerous, 

 while in many of the pines, such as P. resinosa or P. koraiensis 



..b 



b 



FIG. 24. PINUS REFI.EXA. Medullary ray showing (a) the form and disposition 

 of the pits on the lateral walls ; (/>) the ray tracheids. x 280 



or P. reflexa (fig. 24), they attain to maximum size and occupy 

 nearly the entire surface of the wall within the limits of a wood 

 tracheid, thereby becoming few in number. In Sequoia (fig. 25) 

 or Taxodium (fig. 20) they are typically oval, in Pinus cubensis 



Fir.. 25. SEQUOIA GIGANTEA. Medullary ray showing the form and disposition 

 of the pits on the lateral walls. X 280 



or P. taeda (fig. 26) they are variously lenticular, while in P. resi- 

 nosa or P. koraiensis they are oval or oblong, or even quad- 

 rangular. Such variations as a whole are far more numerous 

 and sharply defined in Pinus than in any other genus known. 

 In all the investigated genera the pit is bordered. This finds 



