. Botany for high schools. Botany. LEAVES, THEIR FORM AND MOVEMENT 75 3. FALL OF THE LEAF. 124. Leaves are not permanent outgrowths of the stem as most branches are. Their origin is superficial as compared with the origin of a branch, and they sooner or later fall away from the stem. In many trees and shrubs the leaves formed during the growing season fall at its close. These trees and shrubs are said to be deciduous. The stems remain bare during the resting season which in our climate is the w^inter season. In the spring new leaves are again formed on the new shoots. Other trees and shrubs ho
. Botany for high schools. Botany. LEAVES, THEIR FORM AND MOVEMENT 75 3. FALL OF THE LEAF. 124. Leaves are not permanent outgrowths of the stem as most branches are. Their origin is superficial as compared with the origin of a branch, and they sooner or later fall away from the stem. In many trees and shrubs the leaves formed during the growing season fall at its close. These trees and shrubs are said to be deciduous. The stems remain bare during the resting season which in our climate is the w^inter season. In the spring new leaves are again formed on the new shoots. Other trees and shrubs hold each season's crop of leaves for several (two to four or more) years, and usually one crop, the oldest, falls away each year. These trees and shrubs are said to be ever- gr^^w, because they are holding several crops of green leaves during summer and winter, as in the pines, spruces, firs, balsams, rhododendrons, etc. When the time has come for the leaf to fall, a separation layer of cells is formed at the junction of the petiole with the stem, and the leaf falls away leaving a scar (the leaf scar) on the stem with a smooth surface (Chapter VIII). The scars, therefore, enable us to determine the position and arrangement of the leaves of decid- uous shrubs and trees during the winter. 4. ARRANGEMENT OF LEAVES. 125. The arrangement of leaves on the stem seems to follow certain definite laws, and, barring accidents, is always the same for a given species. 126. Opposite leaves.—Leaves are opposite on the stem when two arise at the same level, or node, but on opposite sides. The milkweed {Asclepias) is a good example, but there are many. Fig. 69. Shcx)t of white pine with "needle" Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Atkinson, George Francis, 1854-1918. New York, H. Holt and Comp
Size: 1629px × 1533px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
