38 TREES IN WINTER 



northeastern United States that is evergreen, and the Larch is our 

 only conifer that is deciduous. Some trees, however, like certain 

 species of Magnolia, are deciduous in New England and evergreen 

 in the southern states. 



The bare-twigged condition prevents the tree from suffering a 

 more rapid loss of water than its roots could suppply in the winter 

 season if the broad, thin leaves were left exposed to evaporation. In 

 the autumn the living substance of the leaf is broken up and with 

 all the food remaining is withdrawn into the branches. Only the 

 framework remains and the colors left by the disintegration of the 

 green chlorophyll. The leaf has served its function as a machine 

 for the manufacture of plant food and is now ready for the scrap 

 heap. Before it dies, however, a separating layer forms at the base 

 of the leaf stalk and heals the wound before the leaf is abstricted. 

 Cold or dryness may hasten the process, but an early frost may kill 

 the leaves and prevent their falling in the normal fashion. 



Not only the fall of leaves but also their autumn coloring is gen- 

 erally independent of frost and may at times occur even in mid- 

 summer. The trees of the northeastern United States show a more 

 brilliant coloring than those in the more humid climate of Europe, 

 and even our native species are said to have duller foliage when 

 grown abroad. 



The Stem — The stem of a tree has the function of connect- 

 ing the roots with the leafy crown and of raising the latter above 

 the shade of competing forms. A branchlet of the Horse-chestnut 

 (fig. 20) may be taken as a convenient form to illustrate the vari- 

 ous markings found on a young stem. The large triangular patches 

 resembling somewhat closed horse-shoes in shape are the leaf-scars 

 showing where the bases of the leaf-stalks were attached to the twig 

 before their fall. The little dots corresponding to the nail holes 

 in a horse-shoe are the hundle-scars and mark the location of the 

 so-called fibro-vascular bundles that run through the leaf -stalks and 

 connect with the veins of the leaf acting thus as the channels for 

 the transference of raw material and manufactured food to and 

 from the leaf. The leaf-scars are located at the nodes and the por- 

 tion between the nodes is called the internode. Scattered 

 along the twig are little dots, the lenUcels, which are openings that 

 function to a certain extent like breathing pores. 



