. Cyclopedia of farm crops. Farm produce; Agriculture. 16 THE PLANT: ITS STRUCTURE, LIFE - PROCESSES AND ENVIRONMENT which remain alive after the sieve cells are apparently dead; their function is not clearly understood. In dicotyledonous plants, between the wood and the bast is found the cambium, an embryonic tissue that forms new cells whose growth causes the stem to thicken year by year. The inner part of this growth becomes wood, which adds an "annual ; These rings are clearly marked, because the wood formed in the fall is denser and has smaller cells than that formed in the
. Cyclopedia of farm crops. Farm produce; Agriculture. 16 THE PLANT: ITS STRUCTURE, LIFE - PROCESSES AND ENVIRONMENT which remain alive after the sieve cells are apparently dead; their function is not clearly understood. In dicotyledonous plants, between the wood and the bast is found the cambium, an embryonic tissue that forms new cells whose growth causes the stem to thicken year by year. The inner part of this growth becomes wood, which adds an "annual ; These rings are clearly marked, because the wood formed in the fall is denser and has smaller cells than that formed in the spring. The outer part of the new growth becomes , which wears away on the outside almost as fast as it forms within, and, in consequence, does not thicken much from year to year. Monocotyledonous stems have no cambium and do not grow thicker from year to year. The cambium causes the cion to unite to the stock; it heals wounds, such as are made by pruning, by forming a tissue called callus. This sometimes produces new , whose growth com- pensates for the part cut away. At the tip of the stem the cambium does not form a complete ring but is confined to the bundles. In trees and shrubs it gradually extends itself from one bundle to another, thus forming a complete ring. As soon as this is accomplished, it begins to form a complete ring of wood within and of bast without. In herbs no such complete ring is formed. Outside the bast is found the rind or cortex, which is usually green, and, in consequence, manu- factures starch. It also serves to convey starch. This is easily seen when it is cut away all around the tree, in the process of " ringing," whereupon the tissues below lose their starch. If the bast be cut through also, the supply of proteids is cut off and death soon ensues. As the stem grows older, layers of cork are formed in the rind. These cut off the tis- sues lying outside them, which soon die and so form bark. The very first layers
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectagriculture, bookyear
