The Primary Structure of the Root

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Introduction: This is the first of two labs that focus on each of the three higher plant organs (root, stem, leaf). It is assumed that you have already learned about tissue and cell types. If not, you should review Cells and Tissues of the Plant Body. The primary body of the root = the structure of th eroot at the end of primary growth. There are two basic objectives that are integrated with the lecture for all three of these labs:

In most plants, the root must fulfill two fundamental roles: absorption of water and nutrients, and anchorage. Further, in many plants, roots function to store food.

Root tip morphology: The apical meristem of the root produces new cells. Some derivatives of the apical meristem become part of the root cap and eventually slough off. Others become organized into one of the three primary meristematic tissues (protoderm, ground meristem, procambium).

Cross Sections of a Herbaceous Dicot Root: Ranunculus (buttercup) roots have a central cylinder of vascular tissue surrounded by a region of ground tissue called the cortex. The cortex is a broad region of cells, the innermost layer of which is called the endodermis. The outermost layer of the vascular tissue (directly inside the endodermis) is called the pericycle.

Origins of Lateral Roots: Lateral roots arise from inner tissues of the root (endogenously), specifically from the pericycle.

Effect of IBA on root formation. IBA is an auxin that stimulates root formation in cuttings. On March 3 and 4 two groups of Coleus cuttings were planted in perlite in each lab. One group was treated with IBA and the other was not. On March 17 these were removed from the perlite and photographed in groups. You may download these photographs below to prepare for your oral presentation:

From Room 118

From Room 122




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