Trees of New York State 43 



General WINTER CHARACTERS 



With the approac'li of winter and the cessation of growth 

 necessitated by it, biennial and perennial plants make definite 

 ];rovision to meet the rigors of the unfavorable season. Freezing 

 temperatures have a drying effect on plant tissue in that the ice 

 crystals start to form in the intercellular space (chinks) between 

 cells rather than in the interior of the cell proper. Death may 

 finally ensue through desiccation resulting from the removal of 

 too much water from living cell contents as these crystals enlarge, 

 rather than from the direct chilling action of low temperatures. 

 Aiborescent plants protect themselves from excessive transpira- 

 tion during the winter montiis and resultant winter-killing as 

 follows : 



1. Leaf-fall. 



2. Production of winter buds which are protected by bud- 



scales, gums, waxes, pubescence, etc. 



3. Completion of growth in length and thickness and 



"hardening" of the new tissue ere cold weather 

 sets in. 



4. Increase in the osmotic pressure of cell sap, requiring 



lower temperatures to permit of the extraction of water 

 from the cells. 



5. Production of corky layers (periderm) on twigs and 



bole. 



(Jrowth in length versus Growth in Thickness 



With the reawakening of growth in the spring, trees begin to 

 grow in height and in thickness. Growth in thickness goes on 

 throughout the whole length of the tree, including the roots, and 

 has its inception in the activities of a growing layer (cambium) 

 underlying the bark, the cells of which begin to divide and form 

 new tissue. Growth in length is confined to the twig- and root-tips 

 and results from buds which are either terminal or near the twig 

 apices. As these buds unfold the embryonic parts contained 

 within elongate and assume their final size. The number of new 

 nodes and internodes resulting from the opening of a bud varies 

 largely with the species and vigor of the individual. In some 

 cases all of the growth for the following season is found in the 

 embryonic condition in the bud and, as the bud opens, merely 

 enlarges to its permanent size. In the majority of cases, however, 

 there are a number of embryonic nodes and internodes included 



