Proceedings of the American Academy of Arts and Sciences. 



Vol. 54. No. 2. — Septp^mber, 1918. 



SIZE VARIATIOX IX TRACE EARY CELLS: 



I. A COMPARISON BETWEEN THE SECONDARY XYLEMS 



OF VASCULAR CRYPTOGAMS, GYMNOSPERMS 



AND ANGIOSPERMS. 



By I. W. Bailey and W. W. Tupper. 



