1908] DORETY—CERATOZAMIA 209 



apical point of the scale leaves. At irregular intervals along the 

 petiole are other, even smaller points. The first leaves are opposite, 

 but the later ones assume the spiral phyllotaxy represented in fig. 12. 



ANATOMY 



As was above noted, the edges of the cotyledon close in after the 

 exit of the plumule, the two halves of the ad axial face meeting in a 

 plane represented by the line ad in fig. 13. Three bundles enter 

 the cotyledon from the vascular plate, and each dichotomizes again 

 and again (fig. 16), the median one being no more a "double" bundle 

 than any of the others. The number of traces may be increased 

 to fifteen toward the upper portion, but is gradually reduced again 

 toward the tip, some bundles approximating in pairs, others dying 

 out. Those in the lobes disappear lower down than the others 

 (fig. 13). The bundles are collateral throughout the cotyledon, and 

 their orientation is normal, as seen in figs. 13, 14, 13, where the 

 xylem faces the line ad. The wood is mesarch (fig. 17), with the 

 protoxylem gradually moving out toward the phloem as it ascends. 

 In the upper portion centrifugal elements are wanting, that is the 

 wood is exarch (fig. 18). The vascular system of the cotyledon is 

 differentiated relatively early in the development of the seedling. In 

 that from which fig. iq was drawn, in which no root has yet appeared, 

 the vessels are fully matured. Worsdell's transfusion tissue was 

 frequently observed in direct continuation with the centripetal xylem 



(fig- 18,*). 



Mucilage canals are numerous in the lower part, and seem to bear 



no definite relation to the strands (figs. 30^ 31) ; farther up they usually 



number one more than the strands and alternate with them ; higher 



still they die out irregularly; in some cotyledons they are absent 



altogether. 



The vascular plate of the hypocotyl axis is irregularly four-sided 



as seen in cross-section; all the xylem is in the center, sometimes in 



a solid mass, sometimes interspersed with pith cells. The protoxylem 



points are clearly distinguishable. In the plant from which fig. 20 



was drawn, the protostelic condition persisted through a vertical 



distance of i.6 mm . Above this the pith cells occupy the central 



region, so that a siphonostele replaces the protostele (fig. 28). About 



