Contents

08 January 2016
Vol 351, Issue 6269

About The Cover

Cover image expansion

COVER Tree of portal blood vessels in the murine fetal liver at embryonic days 12 (bottom left), 13 (bottom right), and 14.5 (top), reconstructed in three dimensions from serial cryosections of portal vasculature. Branch surface area is scaled according to fractal geometries, together with the number of hematopoietic stem cells (HSCs; yellow spheres), suggesting that HSC niche expansion is related to portal vessel surface area. See pages 126, 139, and 176.
Data visualization: Valerie Altounian/Science; base meshes created by Jalal Khan (Icahn School of Medicine at Mount Sinai) using MeshLab