Trichome

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Trichome

Trichomes, from the Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
meaning "growth of hair

Hair

Hair is a protein filament that epidermal growth from hair follicle deep within the dermis. The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats....
", are fine outgrowths or appendages on plant

Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s and certain protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s. These are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae.

ain—usually filamentous—algae, have the terminal cell

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
produced into an elongate "hair-like" structure called a trichome.

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Encyclopedia

Trichomes, from the Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
meaning "growth of hair

Hair

Plant

Protist

Algal trichomes

Certain—usually filamentous—algae, have the terminal cell

Cell (biology)

Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
.

Plant trichomes

Aerial surface hairs

Trichomes on plants are epidermal outgrowths of various kinds. The terms emergences or prickles
Spine (botany)

Spines are leaves that have been modified into cylindrical, hard structures with sharp ends. They are occasionally called thorn , which is incorrect ....
refer to outgrowths that involve more than the epidermis. This distinction is not always easily applied (see Wait-a-minute tree). Also, there are nontrichomatous epidermal cells that protrude from the surface.

A common type of trichome is a hair. Plant hairs may be unicellular or multicellular, branched or unbranched. Multicellular hairs may have one or several layers of cells. Branched hairs can be dendritic (tree-like), tufted, or stellate (star-shaped).,

A common type of trichome is the scale or peltate hair: a plate or shield-shaped cluster of cells attached directly to the surface or borne on a stalk of some kind.

Any of the various types of hairs may be glandular.

In describing the surface appearance of plant organs, such as stems

Plant stem

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaf, inflorescence , conifer cones or other stems etc....
and leaves

Leaf

In botany, a leaf is an above-ground plant Organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin, to expose the cells containing chloroplast to light over a broad area, and to allow light to penetrate fully into the tissues....
, many terms are used in reference to the presence, form, and appearance of trichomes. The most basic terms used are glabrous—lacking hairs— and pubescent—having hairs. Details are provided by:

glabrous, glabrate – lacking hairs or trichomes; surface smooth
hirsute – coarsely hairy
hispid – having bristly hairs
downy – having an almost wool-like covering of long hairs
pilose – pubescent with long, straight, soft, spreading or erect hairs
puberulent – minutely pubescent; having fine, short, usually curly, hairs
pubescent – bearing hairs or trichomes of any type
strigillose – minutely strigose
strigose – having straight hairs all pointing in more or less the same direction as along a margin or midrib
villosulous – minutely villous
villous – having long, soft hairs, often curved, but not matted

Hairs on plants are extremely variable in their presence across species, location on plant organs, density (even within a species), and therefore functionality. However, several basic functions or advantages of having surface hairs can be listed. It is likely that in many cases, hairs interfere with the feeding of at least some small herbivores and, depending upon stiffness and irritability to the "palate", large herbivores as well. Hairs on plants growing in areas subject to frost keep the frost away from the living surface cells. In windy locations, hairs break-up the flow of air across the plant surface, reducing evaporation. Dense coatings of hairs reflect solar radiation, protecting the more delicate tissues underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud drip, hairs appear to enhance this process.

Root hairs

Root hairs, the rhizoid

Rhizoid

Rhizoids are a structure in plants, fungi and some other organisms that functions like a root in support or absorption.In fungi, rhizoids are small branching hyphae that grow downwards from the stolons that anchor the fungus....
s of many vascular plant

Vascular plant

Vascular plants are those plants that have lignin tissue for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms....
s, are tubular outgrowths of trichoblasts, the hair-forming cells on the epidermis of a plant root

Root

In vascular plants, the root is the organ of a plant body that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial root or aerating ....
. That is, root hairs are lateral extensions of a single cell and only rarely branched. Just prior to the root hair development, there is a point of elevated phosphorylase

Phosphorylase

Phosphorylase is a family of Allosteric regulation enzymes that catalysis the production of polyglucose such as glycogen, starch or maltodextrin from a glucose-1-phosphate....
activity.

Root hairs vary between 5 and 17 micrometres in diameter, and 80 to 1,500 micrometres in length (Dittmar, cited in Esau, 1965).

Root hairs can survive for 2 to 3 weeks and then die off. At the same time new root hairs are continually being formed at the top of the root. This way, the root hair coverage stays the same.

It is therefore understandable that repotting must be done with care, because the root hairs are being pulled off for the most part. This is why planting out may cause plants to wilt.

Trichome

Algal trichomes

Plant trichomes

Aerial surface hairs

Root hairs

See also