What vegetative methods are to be followed for propagation of various plants of economic importance?
Answers
1. By death of older parts:
This method of vegetative propagation is commonly found in many bryophytes. In Riccia, Marchantia, Anthoceros, Notothylas and others the progressive death and decay of older parts reach to the dichotomy and two branches are resulted; each of such branches may develop into a new plant.
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2. By branch tips:
According to Smith, in the regions of prolonged drought, all parts of a gametophyte but the branch tips are killed. Each such branch tip is capable to give rise to a new plant on the approach of favourable conditions. This method is quite common in Riccia.
3. By adventitious branches:According to Cavers (1904) several species of Riccia produce adventitious branches from the ventral surface of gametophyte; these branches on being detached may result in the formation of new gametophytes. Such adventitious branches have also been recorded from other bryophytes, e.g., Marchantia, Anthoceros sp.
4. By Gemmae:
According to Campbell (1918) even in Riccia glauca, the cell division takes place in the apices of young rhizoids resulting in gemma-like structures which later on develop into new thalli.
In Marchantia and Lunularia the gemmae are produced in gemma cups situated on the dorsal surface of the gametophyte. Many gemmae are found in each gemma cup. On being detached from the cup, each gemma gives rise to a plant. The gemma cups are circular in Marchantia and crescent-shaped in Lunularia.
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In Anthoceros glandulosus and some other species the gemmae develop on the margin and dorsal surface of the thallus. Each gemma germinates into a new plant.
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In Funaria, small, multi-cellular, linear green gemmae are borne at the leaf apices, shoot apex and on the rhizoids. Such gemmae also develop on the protonema of Funaria hygrometrica. Each gemma is capable to give rise to a new plant. The underground gemmae are known as bulbils.
5. By tubers:
Many bryophytes reproduce vegetatively by means of tubers. The tubers are formed on the margins of the thalli of Riccia discolor, R. billardieri, Anthoceros halli, A. pearsoni. The tubers are borne upon stalks on the ventral surface of Anthoceros himalayensis. They are found near the growing points of the thallus in A. laevis. The tubers germinate into new thalli on the approach of favourable conditions.
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6. By primary protonema:
In Funaria the primary protonema are produced with the result of the germination of the spore. The protonema may break into small pieces; and each such fragment is capable to grow into a new protonema. The protonema bears many buds. Each bud develops into a new plant.
7. By secondary protonema:
The protonema formed by other methods, than from the germination of the spore, are known as secondary protonema. Morphologically they are quite alike to primary protonema. The secondary protonema may develop from the exposed rhizoid or any other detached living part of the gametophyte. These protonema also produce buds which develop into gametophytes. This method of vegetative reproduction is very common in Funaria hygrometrica.