46 GYMNOSPERMS 



zone of wood, reaching, near the base of the trunk, a radial thickness 

 of 8 cm. Growth-rings in this specimen are very distinct. Wie- 

 LAND**" thinks the trunk is polyxyHc, although he admits that there 

 may have been a persistent cambium. His excellent photograph of 

 the transverse section is so identical with the appearance of Dioon 

 spinulosum and Dioon cdulc, where the rings are undoubtedly formed 

 by a persistent cambium, that we feel certain that the same condition 

 is present in Cycadeoidea jenneyana. Besides, the polyxylic condi- 

 tion, with its successive cambiums in the living cycads, where it is 



Fig. 39. — Cycadella sp. : transverse section of top of small trunk from Wyoming, 

 showing large pith, woody cylinder, and cortex; m, pith; .v, xylem; c, cambium; cb, leaf 

 traces; r, ramentum; h, leaf (or peduncle) traces; /, base of leaf; natural size. — After 



WlELAND.*^ 



well known, makes the successive zones or rings look very different 

 from the growth-rings formed by a persistent cambium. Scott says 

 that in Cycadeoidea yatesii there is evidence for the presence of two 

 or more zones of xylem and phloem, like those in Cycas. Whether 

 the rings, whatever their character, are annual, may be very doubt- 

 ful, for, in the living cycads, rings looking very much like those of 

 Cycadeoidea jenneyana may be formed every other year, or at inter- 

 vals of 20 years or more. 



The leaf-trace bundles pass directly through the cortex into the 

 leaves, there being none of the girdling which is such a prominent 

 feature of the living cycads. There are no bundles in the pith, nor, 

 with axillary cones, would any be anticipated. However, there are 



