Lab Girl

by Hope Jahren

In order to prepare for their long winter journey, trees undergo a process known as “hardening.” First the permeability of the cell walls increases drastically, allowing pure water to flow out while concentrating the sugars, proteins, and acids left behind. These chemicals act as a potent antifreeze, such that the cell can now dip well below freezing and the fluid inside of it will still persist in a syrupy liquid form. The spaces between the cells are now filled with an ultra-pure distillate of cell water, so pure that there are no stray atoms upon which an ice crystal could nucleate and grow. Ice is a three-dimensional crystal of molecules, and freezing requires a nucleation spot—some chemical aberration upon which the pattern may start to build. Pure water devoid of any such site may be “super-cooled” to forty degrees below zero and still remain an ice-free liquid. It is in this “hardened” state, with some cells packed full of chemicals and others sectioned off for purity, that a tree embarks on its winter journey, standing unmoved through the frost, sleet, and blizzards of the season.