_a."_ Pores crowded, occupying nearly all the space between pith rays. _a.'"_ Color yellowish white, often with a greenish tinge in heart-wood ........................TULIP POPLAR. CUCUMBER TREE. _b.'"_ Color of sap-wood grayish, of heart-wood light to dark reddish brown ......................SWEET GUM. _b."_ Pores not crowded, occupying not over one-third the space between pith rays; heart-wood brownish white to very light brown .........................BASSWOOD. _b._ Pith rays scarcely distinct, yet if viewed with ordinary magnifier, plainly visible. _a.'_ Pores indistinct to the naked eye. _a."_ Color uniform pale yellow; pith rays not conspicuous even on the radial section .....BUCKEYE. _b."_ Sap-wood yellowish gray, heart-wood grayish brown; pith rays conspicuous on the radial section. SOUR GUM. _b.'_ Pores scarcely distinct, but mostly visible as grayish specks on the cross-section; sap-wood whitish, heart-wood reddish ..............................BIRCH. D. Pith rays not visible or else indistinct, even if viewed with magnifier. 1. Wood very soft, white, or in shades of brown, usually with a silky luster .................................COTTONWOOD (POPLAR). ==== ADDITIONAL NOTES FOR DISTINCTIONS IN THE GROUP. Cherry and birch are sometimes confounded, the high pith rays on the cherry on radial sections readily distinguishes it; distinct pores on birch and spring wood zone in cherry as well as the darker vinous-brown color of the latter will prove helpful. Two groups of birches can be readily distinguished, tho specific distinction is not always possible. 1. Pith rays fairly distinct, the pores rather few and not more abundant in the spring wood: wood heavy, usually darker, CHERRY BIRCH and YELLOW BIRCH. 2. Pith rays barely distinct, pores more numerous and commonly forming a more porous spring wood zone; wood of medium weight, CANOE OR PAPER BIRCH. [Illustration: Fig. 136. Wood of Beech, Sycamore and Birch.] The species of maple may be distinguished as follows: 1. Most of the pith rays broader than the pores and very conspicuous ........................................SUGAR MAPLE. 2. Pith rays not or rarely broader than the pores, fine but conspicuous. _a._ Wood heavy and hard, usually of darker reddish color and commonly spotted on cross-section ...............RED MAPLE.