Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] BUDS AND STEMS 105 rangement of leaves within the bud is known as vernation. An interesting piece of field and laboratory work is the comparison of vernation in a number of different buds. Those of the wild cherry, birch, European walnut, snowball, lilac, and tulip tree are of in- terest for this purpose. Why buds are Covered.— When we consider that most of our earliest green leaves come from opening buds in the early spring, the im
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] BUDS AND STEMS 105 rangement of leaves within the bud is known as vernation. An interesting piece of field and laboratory work is the comparison of vernation in a number of different buds. Those of the wild cherry, birch, European walnut, snowball, lilac, and tulip tree are of in- terest for this purpose. Why buds are Covered.— When we consider that most of our earliest green leaves come from opening buds in the early spring, the impor- tance of a protective cover- ing is well seen. Nevertheless buds are frozen time and again during the cold weather, only to thaw out again without in- jury to the plant. Sudden changes, however, do much harm. Some buds do not open during mild winter weather when temperature conditions are seemingly favorable; a definite length of growth seems in that case to be necessary. During warm weather plants give rise to buds which are devoid of protective scale leaves. Such is also noticed in tropical forms, which are not called upon to meet rigorous cli- matic conditions. We have now learned something about the outside markings of a branch.^ Let us turn our attention to the in- ternal structure of the horse-chestnut stem to see how the parts within are adapted to perform the work which they do. Study of a Dicotyledonous Stem. — In the cross section of horse-chestnut twig, notice the innermost part, the pith. See if it is as tough as the wood of the stem. About what proportion of the cross section is occupied by the wood? Everything outside of the wood is collectively known as the Section across a young twig of box elder, bark. It is made up of three layers, showing the four stem regions; e, epi- Pull off outer layer; notice Its color, dermis, represented by the heavy bound- ing hne; c. cortex; w, wood; p, pith. ^ See Hunter and Valentine, Manual. (From Coulter, Plant Relations
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