STOKRS AGRICULTURAL EXPERIMENT STATION. 319 



off. in thin papery layers. In the Birches (p. 423) and Cherries 

 (p. 503) the breathing pores (lenticels) become horizontally elon- 

 gated to form narrow transverse streaks which are characteristic for 

 these forms. When ridges or scales are formed they may be close 

 and firm and with difficulty removed from the trunk as is the case 

 with the bark in the Black Oak group or, on the other hand, they 

 may be easily rubbed off as are the scales of the bark of the 

 White Oak and of most members of the White Oak group. Bark 

 of this latter type is called -flaky in our descriptions and this 

 distinction between barks that are flaky and those that are not 

 flaky is of considerable importance in classification. To avoid 

 confusion little notice is taken of the minute scales that are 

 likely to occur on the surface of both types of bark. The bark 

 may come off in large sheets as in the Shag-bark Hickory (p. 403) 

 and the Sycamore (p. 483), and the ridges may be long as in 

 the Chestnut (p. 431) or short and run together to form more 

 or less perfect diamond-shaped areas as in the White Ash (p. 557) 

 but these as well as other differences in the sculpturing are shown 

 in the photographs and do not require further discussion in the 

 introduction. 



TWIGS The unqualified word twig refers in the descriptions 

 to the growth of the past season only. Older twigs and branch- 

 lets are the designations employed for the small growth of several 

 seasons. The Horse-chestnut (fig. 4) may be taken as a convenient 

 form to illustrate the various markings found on the twig. 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 bundle-scars 

 and mark the location of the so-called fibro- vascular bundles that 

 run up 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 portion between the nodes is called 

 the internode. Scattered along the twig are little dots, the lenticels, 

 which are openings that function to a certain extent like breathing 

 pores. Above each leaf-scar is normally produced an axillary bud 

 so called because located in the axil or angle made between the 

 twig and the leaf-stalk when the latter was present. The lateral 



