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Marijuana Botany by Robert Connel Clark
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<blockquote data-quote="cannebosanac" data-source="post: 20016" data-attributes="member: 1357"><p>poglavlje 2 nastavak</p><p></p><p>In Cannabis, mitosis takes place in the shoot apex </p><p>(meristem), root tip meristems, and the meristematic cam- </p><p>bium layer of the stalk. A propagator makes use of these </p><p>meristematic areas to produce clones that will grow and be </p><p>multiplied. Asexual propagation techniques such as cuttage, </p><p>layerage, and division of roots can ensure identical popula- </p><p>tions as large as the growth and development of the paren- </p><p>tal material will permit. Clones can be produced from even </p><p>a single cell, because every cell of the plant possesses the </p><p>genetic information necessary to regenerate a complete </p><p>plant. </p><p>Asexual propagation produces clones which perpetu- </p><p>ate the unique characteristics of the parent plant. Because </p><p>of the heterozygous nature of Cannabis, valuable traits </p><p>may be lost by sexual propagation that can be preserved </p><p>and multiplied by cloning. Propagation of nearly identical </p><p>populations of all-pistillate, fast growing, evenly maturing </p><p>Cannabis is made possible through cloning. Any agricul- </p><p>tural or environmental influences will affect all the mem- </p><p>bers of that clone equally. </p><p>The concept of clone does not mean that all members </p><p>of the clone will necessarily appear identical in all charac- </p><p>teristics. The phenotype that we observe in an individual is </p><p>influenced by its surroundings. Therefore, members of the </p><p>clone will develop differently under varying environmental </p><p>conditions. These influences do not affect genotype and </p><p>therefore are not permanent. Cloning theoretically can pre- </p><p>serve a genotype forever. Vigor may slowly decline due to </p><p>poor selection of clone material or the constant pressure </p><p>of disease or environmental stress, but this trend will re- </p><p>verse if the pressures are removed. Shifts in genetic compo- </p><p>sition occasionally occur during selection for vigorous </p><p>growth. However, if parental strains are maintained by in- </p><p>frequent cloning this is less likely. Only mutation of a gene </p><p>in a vegetative cell that then divides and passes on the mu- </p><p>tated gene will permanently affect the genotype of the </p><p>clone. If this mutated portion is cloned or reproduced </p><p>sexually, the mutant genotype will be further replicated. </p><p>Mutations in clones usually affect dominance relations and </p><p>are therefore noticed immediately. Mutations may be in- </p><p>duced artificially (but without much predictability) by </p><p>treating meristematic regions with X-rays, colchicine, or </p><p>other mutagens. </p><p>The genetic uniformity provided by clones offers a </p><p>control for experiments designed to quantify the subtle </p><p>effects of environment and cultural techniques. These </p><p>subtleties are usually obscured by the extreme diversity </p><p>resulting from sexual propagation. However, clonal uni- </p><p>formity can also invite serious problems. If a population of </p><p>clones is subjected to sudden environmental stress, pests, or </p><p>disease for which it has no defense, every member of the </p><p>clone is sure to be affected and the entire population may </p><p>be lost. Since no genetic diversity is found within the </p><p>clone, no adaptation to new stresses can occur through </p><p>recombination of genes as in a sexually propagated </p><p>population. </p><p>In propagation by cuttage or layerage it is only neces- </p><p>sary for a new root system to form, since the meristematic </p><p>shoot apex comes directly from the parental plant. Many </p><p>stem cells, even in mature plants, have the capability of </p><p>producing adventitious roots. In fact, every vegetative cell </p><p>in the plant contains the genetic information needed for an </p><p>entire plant. Adventitious roots appear spontaneously from </p><p>stems and old roots as opposed to systemic roots which </p><p>appear along the developing root system originating in the </p><p>embryo. In humid conditions (as in the tropics or a green- </p><p>house) adventitious roots occur naturally along the main </p><p>stalk near the ground and along limbs where they droop </p><p>and touch the ground. </p><p>Rooting </p><p>A knowledge of the internal structure of the stem is </p><p>helpful in understanding the origin of adventitious roots. </p><p>The development of adventitious roots can be broken </p><p>down into three stages: (1) the initiation of meristematic </p><p>cells located just outside and between the vascular bundles </p><p>(the root initials), (2) the differentiation of these meristem- </p><p>atic cells into root primordia, and (3) the emergence and </p><p>growth of new roots by rupturing old stem tissue and </p><p>establishing vascular connections with the shoot. </p><p>As the root initials divide, the groups of cells take on </p><p>the appearance of a small root tip. A vascular system forms </p><p>with the adjacent vascular bundles and the root continues </p><p>to grow outward through the cortex until the tip emerges </p><p>from the epidermis of the stem. Initiation of root growth </p><p>usually begins within a week and young roots appear within </p><p>four weeks. Often an irregular mass of white cells, termed </p><p>callus tissue, will form on the surface of the stem adjacent </p><p>to the areas of root initiation. This tissue has no influence </p><p>on root formation. However, it is a form of regenerative </p><p>tissue and is a sign that conditions are favorable for root </p><p>initiation. </p><p>The physiological basis for root initiation is well un- </p><p>derstood and allows many advantageous modifications of </p><p>rooting systems. Natural plant growth substances such as </p><p>auxins, cytokinins, and gibberellins are certainly responsible </p><p>for the control of root initiation and the rate of root for- </p><p>mation. Auxins are considered the most influential. Auxins </p><p>and other growth substances are involved in the control of </p><p>virtually all plant processes: stem growth, root formation, </p><p>lateral bud inhibition, floral maturation, fruit development, </p><p>and determination of sex. Great care is exercised in appli- </p><p>cation of artificial growth substances so that detrimental </p><p>conflicting reactions in addition to rooting do not occur. </p><p>Auxins seem to affect most related plant species in the </p><p>same way, but the mechanism of this action is not yet </p><p>fully understood.</p></blockquote><p></p>
[QUOTE="cannebosanac, post: 20016, member: 1357"] poglavlje 2 nastavak In Cannabis, mitosis takes place in the shoot apex (meristem), root tip meristems, and the meristematic cam- bium layer of the stalk. A propagator makes use of these meristematic areas to produce clones that will grow and be multiplied. Asexual propagation techniques such as cuttage, layerage, and division of roots can ensure identical popula- tions as large as the growth and development of the paren- tal material will permit. Clones can be produced from even a single cell, because every cell of the plant possesses the genetic information necessary to regenerate a complete plant. Asexual propagation produces clones which perpetu- ate the unique characteristics of the parent plant. Because of the heterozygous nature of Cannabis, valuable traits may be lost by sexual propagation that can be preserved and multiplied by cloning. Propagation of nearly identical populations of all-pistillate, fast growing, evenly maturing Cannabis is made possible through cloning. Any agricul- tural or environmental influences will affect all the mem- bers of that clone equally. The concept of clone does not mean that all members of the clone will necessarily appear identical in all charac- teristics. The phenotype that we observe in an individual is influenced by its surroundings. Therefore, members of the clone will develop differently under varying environmental conditions. These influences do not affect genotype and therefore are not permanent. Cloning theoretically can pre- serve a genotype forever. Vigor may slowly decline due to poor selection of clone material or the constant pressure of disease or environmental stress, but this trend will re- verse if the pressures are removed. Shifts in genetic compo- sition occasionally occur during selection for vigorous growth. However, if parental strains are maintained by in- frequent cloning this is less likely. Only mutation of a gene in a vegetative cell that then divides and passes on the mu- tated gene will permanently affect the genotype of the clone. If this mutated portion is cloned or reproduced sexually, the mutant genotype will be further replicated. Mutations in clones usually affect dominance relations and are therefore noticed immediately. Mutations may be in- duced artificially (but without much predictability) by treating meristematic regions with X-rays, colchicine, or other mutagens. The genetic uniformity provided by clones offers a control for experiments designed to quantify the subtle effects of environment and cultural techniques. These subtleties are usually obscured by the extreme diversity resulting from sexual propagation. However, clonal uni- formity can also invite serious problems. If a population of clones is subjected to sudden environmental stress, pests, or disease for which it has no defense, every member of the clone is sure to be affected and the entire population may be lost. Since no genetic diversity is found within the clone, no adaptation to new stresses can occur through recombination of genes as in a sexually propagated population. In propagation by cuttage or layerage it is only neces- sary for a new root system to form, since the meristematic shoot apex comes directly from the parental plant. Many stem cells, even in mature plants, have the capability of producing adventitious roots. In fact, every vegetative cell in the plant contains the genetic information needed for an entire plant. Adventitious roots appear spontaneously from stems and old roots as opposed to systemic roots which appear along the developing root system originating in the embryo. In humid conditions (as in the tropics or a green- house) adventitious roots occur naturally along the main stalk near the ground and along limbs where they droop and touch the ground. Rooting A knowledge of the internal structure of the stem is helpful in understanding the origin of adventitious roots. The development of adventitious roots can be broken down into three stages: (1) the initiation of meristematic cells located just outside and between the vascular bundles (the root initials), (2) the differentiation of these meristem- atic cells into root primordia, and (3) the emergence and growth of new roots by rupturing old stem tissue and establishing vascular connections with the shoot. As the root initials divide, the groups of cells take on the appearance of a small root tip. A vascular system forms with the adjacent vascular bundles and the root continues to grow outward through the cortex until the tip emerges from the epidermis of the stem. Initiation of root growth usually begins within a week and young roots appear within four weeks. Often an irregular mass of white cells, termed callus tissue, will form on the surface of the stem adjacent to the areas of root initiation. This tissue has no influence on root formation. However, it is a form of regenerative tissue and is a sign that conditions are favorable for root initiation. The physiological basis for root initiation is well un- derstood and allows many advantageous modifications of rooting systems. Natural plant growth substances such as auxins, cytokinins, and gibberellins are certainly responsible for the control of root initiation and the rate of root for- mation. Auxins are considered the most influential. Auxins and other growth substances are involved in the control of virtually all plant processes: stem growth, root formation, lateral bud inhibition, floral maturation, fruit development, and determination of sex. Great care is exercised in appli- cation of artificial growth substances so that detrimental conflicting reactions in addition to rooting do not occur. Auxins seem to affect most related plant species in the same way, but the mechanism of this action is not yet fully understood. [/QUOTE]
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