Cline

Cline [ Biology ]	Dictionary of botanic terminology - index of names
Adjective: Clinal Adverbs: Clinally

A gradual and sequential change in population characteristics over a geographical area without significant break such as would justify division into separate species.

A cline is a series of contiguous populations in a group of related organisms, usually along a line of environmental or geographic transition, that exhibit gradual and continuous change of character between two extreme in response to some environmental gradient.
Continuous series of differences in function or structure (phenotype) displayed by members of a species over a geographical area along a line that extends from one end of their range to another. The change in phenotype does not result in different species as long as the geographically spread populations can interbreed with one another.

Cline (Clinal belt) [ Biology ]

A region of overlap in the geographical ranges of two species or sub-species capable of inter-breeding.

Often there is a gradient in the physical features and in gene frequencies of the species across the belt due to hybridization. The occurrence of natural hybrids may be more common than we might suppose.

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994