. Nature and development of plants. Botany. 88 NATURE OF LENTICELS some trees the cork cells break off about as fast as they are formed, so that a comparatively thin layer of cork cells remains attached to the trunk. Such trees have a smooth bark, as in the beech. In other cases the cork cells are formed in great abundance, and owing to the adhesion of the cells, thick layers of cork are formed, as in the oaks, and giant trees of the Pacific. It is evident that this mantle of impervious cork cells would tend to prevent the access of the atmosphere to the stem. We have seen that all living cell
. Nature and development of plants. Botany. 88 NATURE OF LENTICELS some trees the cork cells break off about as fast as they are formed, so that a comparatively thin layer of cork cells remains attached to the trunk. Such trees have a smooth bark, as in the beech. In other cases the cork cells are formed in great abundance, and owing to the adhesion of the cells, thick layers of cork are formed, as in the oaks, and giant trees of the Pacific. It is evident that this mantle of impervious cork cells would tend to prevent the access of the atmosphere to the stem. We have seen that all living cells respire. In many instances the air spaces extending from the leaves to all regions of the stem are. Fig. 51. Fig. 52. Fig. 51. Later development of a lenticel: d, cork cambium; i, intercel- lular space. Fig. 52. Surface view of lenticels: A, lenticels on branch of horse-chestnut appearing as minute brownish swellings. B, old lenticels on white .birch appearing as dark lens-shaped streaks. sufHcient to bring about an adequate interchange of gases but in young stems where growth is vigorous and where therefore respiration is considerable, special devices are required to bring the living cells of the stem into more direct communication with the air. This work is effectively accomplished in herbaceous stems by the stomata, but in stems characterized by the forma- tion of cork it is noticed that the cells just below the stomata begin to divide and form a rather loose mass of cells that lift up and finally rupture the tissues about the stomata, thus forming a small, lens-shaped outgrowth on the surface of the young stem, called a lenticel (Figs. 50; 52, A). Soon this growth becomes. 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 Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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