Elementary Notes on Structural Botany (Classic Reprint)
by A H Church (9781330208496)

Elementary Notes on Structural Botany (Classic Reprint)
 
A H Church
Format: Paperback / softback
Pages: 38
Category: Biology, Life Sciences
Publisher: Forgotten Books
ISBN: 9781330208496
ISBN-10: 1330208498



Excerpt from Elementary Notes on Structural Botany A typical Land Plant, as derived from submarine vegetation, is a more complex organism in that the first problem is how to obtain sufficient Nitrates, Phosphates, and other compounds as 'food-salts' to carry out proteid-synthesis, when these are only present in the soil. This involves the necessary differentiation of an absorbing root in the ground, with subaerial shoot; the function of the latter being to produce and display as much body-surface as possible to air and sunlight. Since the absorbing cells are in a solution of soil-water (often little better than tap-water), a current has to be maintained from the roots to the leaves (Transpiration-current), and enormous quantities of water require to be evaporated at the surface of the leaves (Transpiration). Hence the Primary distinction in land-plants of Leaves, Stem, and Root: the first being the essential photosynthetic and proteid-synthetic regions of the organism. The Leaf is the Laboratory of the Plant; with conductive system leading to it, as also away from it, in the form of definite strands of vascular tissue known as Vascular Bundles (V.B.) of Xylem and Phloem. The main axis normally grows erect, at right angles to the surface of the ground, to give optimum space-distribution; bearing leaves as laminate extensions of the soma, and branches repeating similar organization; thus giving a 'tree habit' of diffused growth spread over considerable space, as opposed to the concentrated and condensed body of a locomotile animal. The Plant-axis also exhibits continuous growth, by definite 'growing-points', which may go on producing new leaves and new axes so long as nutrition is satisfactory; i.e. the plant continues to grow at the ends. Growing Point: essentially a mass of undifferentiated growing and dividing cells (meristem); exhibiting phases of (1) centric growth, i.e. around a point; (2) unilateral distribution, i.e. on one side only; maintaining the growing apex at the end of a longitudinal axis; (3) retarded, since the stem attains a definite 'adult' size. Increase is effected by the growth and sub-division of each individual cell in irregular sequence: any cell may be dividing, but the general effect and dome-shaped outline are retained; i.e. the mass grows as a whole, and all the protoplasts are in living communication, as typical parenchymatous cells, or in this case, embryonic tissue, practically immortal, and including generalized germ-plasm. Mechanism of Cell-Division: The nucleus divides first, presenting phenomena of Mitosis: In higher plants and animals the nucleus presents complex organization of plasmic ground-substance, with fluid in vacuolations, and framework of linin, with chromatin distributed in a reticulum of chromosomes. The latter are of constant number for a given species, and display a certain degree of individuality, being capable of independent division by longitudinal fission. The mass of the nucleus is fluid, and is held in spherical form among the cell-cytoplasm by surface-tension, and is covered by a plasmatic film (nuclear membrane), as its 'resting-stage' in the metabolizing cell. In Mitosis the membrane disappears; the linin arranges a 'spindle-mechanism', with 'spindle-fibres' from two 'poles', and the chromosomes separate (prophase), arrange in the 'equatorial plate', and each divides: spindle-fibres attach to the halves, and the 'daughter-chromosomes travel to the poles (anaphase), there uniting to build the new reticulum of the 'daughter nuclei' (telophase). In the equatorial plane, across the central spindle-fibres, a zone of demarcation of the fields of the two new centres is marked by a deposit of polysaccharide waste, as the first indication of the dividing wall: this extends to the older walls, and constitutes the primary septum. Later deposits of cellulose on this wall commonly present cleavage-effects, with the production of intercellular spa.

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