The Ascent of Sap 125 



itself from the protoplasm and withdraws into the 

 little spaces between the wood-cells. There it 

 freezes, making tiny crystals of ice. A winter 

 bough, broken across, will be found full of them. 

 They sparkle in a strong light like diamond dust. 



The protoplasm, having parted with so much 

 water, is much denser in winter than it was in 

 summer. It becomes a stiff jelly, and in this dry 

 state it can live on through bitter weather. 



There are some gases in living wood, and these 

 are contracted by the cold. The whole contents 

 of the bough have gone into winter quarters. 



If we cut off a spray of sugar maple when the 

 thermometer is at zero, or thereabouts, the cut 

 end, examined out of doors, will appear quite dry. 

 But if the twig is taken into a warm room and 

 kept there for a quarter of an hour, the little ice 

 needles between the cells thaw out. Then the 

 gases expand in the warmth, and by their expan- 

 sion help to push fluid out of the wood and the 

 broken end of the twig begins to drip. The heat 

 of the house has done for the broken twig indoors 

 just what the warm sunshine did for the broken 

 branches out of doors. 



When spring draws near, " the vital move- 

 ment " of the sap begins. The root-tips, far below 

 the frost line, awaken. They grow a new work- 

 ing outfit of root-hairs, and begin to drink earth- 

 water from lower layers of soil, though perhaps 

 the surface of the ground is still frozen. Mean- 



