Root hair length

Assumed to extend the root plane by the root hair length Sink term in model... 

In addition to reduction in root length, seedlings exposed to all concentrations of polar peak 1B displayed both an increase in root hairs and chlorosis at the tips of the cotyledons. The severity of these symptoms increased with the dosage. 

Compare the surface to volume ratios for an E. coli cell, a liver cell, the nucleus of a eukaryotic cell, a root hair. If a cell of 20 pm diameter is 20% covered with microvilli of 0.1 pm diameter and 1 pm length centered on a 0.2 pm spacing, how much will the surface/volume ratio be increased ... 

Hydrophytes. The effect of an aquatic environment on the structure of water plants is most striking. The root systems are reduced both in length and number of branches. The root hairs of those immersed in the water are absent. The supportive action of the water is such that the fibrovascular elements of the stems, which usually function both, for support and conduction of crude sap, are greatly reduced in size and strength. The leaves, stems and roots possess large air-spaces. The mesophyll of the leaves is. 

The entire root system of a single plant, exclusive of root hairs, totalled 13,815,672 members with a surface area of approximately 2,554 sq. ft. The combined length of all roots was 387 miles, distributed as follows main roots, O.04 miles secondary roots, 3.37 miles tertiary roots, 108.74 miles and very fine quaternary roots, 275 miles. 

THE NUMBER, LENGTH AND SURFACE OF THE ROOTS, OTHER THAN ROOT HAIRS, ON A SINGLE RYE PLANT (from DITTMER, 1937)... 

Determinations of the extent of root development of oats, rye, and bluegrass under field conditions were subsequently made by Dittmer (1-938). In this study core samples were taken to a depth of 6 inches and the number and length of the roots and root hairs measured. These data are given in Table 16.IV. Although the root development per unit volume of soil was less under these field conditions than in the greenhouse, the total for the three crops, especially of bluegrass, are very impressive. 

Pavlychenko states that the extent of development of the fine root structures was amazing. Roots that were only about a tenth of a millimeter in diameter grew through hard soil to a distance of 185 cm or more, and each branch from the main roots developed 600—700 finer branches. One nodal root of crested wheatgrass together with its branches attained a total length of 17.7 miles. Data for root hairs were not reported. 

Among the first to consider root hairs in their model were Bhat et al. (1976) and Itoh and Barber (1983), while attempting to explain experimentally obtained P uptake values exceeding those calculated by one of the previously available models. Three principal approaches to integrate root hairs into a rhizosphere model are found in the literature (1) The boundary where exudation and uptake occurs is extended by the length of the root hairs (e.g. Kirk, 1999) (2) The continuity equation for root uptake is extended with a separate sink term (e.g. Geelhoed et al., 1997) and (3) The transport equation is solved in a three-dimensional model with cylindrical coordinates (Geelhoed et al., 1997). 

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