1919] 



MILLER— CYC AS MEDIA 



219 



are absent. Bundles of the former resemble those of the latter 

 in shape, the secondary alignment of the former being disturbed 

 by unequal growth and pressure, and bundles of both are of about 

 equal size, those of the cortical cylinder being a little longer radi- 

 ally. Both cylinders give off leaf traces which differ in respect 

 to the presence or absence of protoxylem and protophloem. 



Other cortical cylinders. — There is little reason for believ- 

 ing that the second and succeeding cortical cylinders would have 



Fig. 10. — Cycas media: radial section of stem, showing centripetal end of second 

 cylinder; c, cortical cells; ph, crushed protophloem of first cylinder; x, innermost 

 xylem elements of cylinder, showing distinct pits, some having fused; X400. 



a mode of origin and development different from that of the first; 

 consequently but little time was devoted to the study of the 

 second cortical cylinder. Preparations from the stem base only 

 were examined, and, as was expected, these showed conditions 

 in the mature part of the stem identical with those of the first 

 cortical cylinder in the same region. Further discussion, therefore, 

 would be but a repetition of what has been recorded thus far. 



In concluding the matter of cortical cylinders it may be well 

 to mention the relationship of their number to the age of the plant. 

 Certainly they do not occupy the position of growth rings, nor 



