Epidermal hairs

Ting and coworkers (Beasley and Ting 1973, 1974, Dhindsa et al. 1976) examined the effects of plant hormones on the growth of cotton fibers in vitro. In fertilized ovules, GA causes a large increase in fiber development while lAA causes a smaller increase. Both kinetin and ABA are inhibitory to fiber development but do not prevent the promotive effect of GA. The authors suggest that the larger promotive effect of GA relative to that of lAA may be due in part to differences in the content of these hormones in the isolated ovules. 

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Quiros, C.F. et al.. Resistance in tomato to the pink form of the potato aphid Macrosiphum euphorbiae. The role of anatomy, epidermal hairs and foliage composition, J. Am. Soc. Hortic. Sci., 102, 166, 1977. 

Cotton fiber is made of the epidermal hairs from seeds of members of genus Gossypium. These fibers consist of hollow cylindrical tubes that are 15-22 pm in diameter, narrowing at one end. The walls of a cotton fiber are made of 90-96% cellulose, mixed with about 5% water and small amounts of pectins, and other impurities. When dried, these tubes are flat and naturally curl or twist like a ribbon. Untreated cotton has from 150 to 300 twists per inch. The fibers are from 0.5 to over 2 inches long, and are extremely thin, from 0.0005 to 0.0009 inches in diameter. 

The types of pubescence active in defense are diverse, ranging from the simple, unbranched or stellate epidermal hairs... 

Root-hair walls consist chiefly of cellulose and calcium pectate in layers continuous with corresponding layers in the epidermal hair-forming cell. There is also evidence for... 

Johnson, B. 1953. The injurious effects of the hooked epidermal hairs of the French bean (Phaseolus vulgaris L.) on Aphis craccivora Koch. Bull. Ent. Res. 44 779-788. 

Various techniques for collection of root exudates are associated with the risk of root injury by rupture of root hairs and epidermal cells or rapid change of the environmental conditions (e.g., temperature, pH, oxygen availability) during transfer of root systems into trap solutions, application of absorbtion materials onto the root surface, and preparation of root systems for exudate collection. The possible impact of those stress treatments may be assessed by measuring parameters of plant growth in plants either. subjected or not subjected to the collection procedure (6) and by comparing exudation patterns after exposure of roots to the handling procedures with different intensity. 

To pass into the skin, the substance must enter through one or more of the following routes the epidermal cells, the sweat glands, the sebaceous glands, or the hair follicles. The pathway through the stratum corneum and the epidermal cells is the main avenue of penetration, as this tissue constitutes the majority of the surface area of the skin. 

It is doubtful whether the insect uses pederin for defensive purposes, because it acts on the skin of animals only when it is crushed and not through mere contact with the insect, even if prolonged. It also has neither insecticidal nor repellent properties (92). However, it causes epidermic necrotization as acute pederosis and desquamation as chronic pederosis on human skin. On the other hand, it stimulates bedsore cicatrization in lower doses and leads to complete healing. Application to mouse skin produces dermatitis with necrosis or huge edema, and the damaged tissue is reconstituted with a permanent loss of hair. 

Plants have served as a food source for fish. Insects, and mammals since early biotic times. In response plants have developed intricate physical as well as chemical protective mechanisms. The two defensive structures that are the primary subject of this chapter are trichomes and glands. Trichomes are epidermal appendages of diverse form and structure, such as protective and glandular hairs and scales or peltate hair. 

Epidermal tissue of plants consists of flat cells, usually containing no chloroplasts, with a thick outer wall covered by a heavy waxy cuticle about 2 pm thick. Only a few specialized cells are found in the epidermis. Among them are the paired guard cells that surround the small openings known as stomata on the undersurfaces of leaves and control transpiration of water. Specialized cells in the root epidermis form root hairs, long extensions ( 1 mm) of diameter 5-17 pm. Each hair is a single cell with the nucleus located near the tip. 

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