8 - PLB 105 Lab ManualFall 2010 page 8-1 Laboratory 8 Root...

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PLB 105 Lab Manual—Fall 2010 page 8-1 Laboratory 8 Root Apical Organization, Primary Growth, Lateral Roots, and Root Systems A. Root Apical Organization After reading the text material and reviewing notes on root apical meristem organization, it should be clear that no single concept of apical organization covers all the possibilities of cell organization found in roots. It should also be clear that some concepts (Apical Cell Theory and Histogen Theory) are not accepted as theories applied to all plant groups. Many plant anatomists and developmental biologists, however, still analyze root apical meristems by the number of initial layers present and by the tissues that differentiate from them. It is useful, therefore, to look at several examples of root apical meristems and to attempt to analyze their organization critically using the theories available. For each root tip provided, determine the type of organization present by carefully examining a median longitudinal section (MLS) of a root tip. Some of the slides contain serial sections, so you will have to find the MLS by scanning several sections. Note also the tissues that differentiate from the tiers or zones and make a diagrammatic drawing of each example. In addition, for each specimen below, determine if the root apex is of the open or closed type of apical organization. 1. Raphanus sativus (radish) root apex—prepared slide Radish is a dicot. Raphanus has the most common histogen type in dicot plants: three tiers of cell-initiating regions (= histogens) give rise to (1) the vascular cylinder, (2) the cortex, and ( 3) the root cap and epidermis. 2.
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8 - PLB 105 Lab ManualFall 2010 page 8-1 Laboratory 8 Root...

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