Life History of an Orchid

The orchid seed is a very simple structure weighing between 6.3 and 0.3 micrograms , between 470 and 560 in length and 80- 129 in width. It does not possess any nutritive tissue ,being composed of the embryo enclosed in a loose air –filled seed coat which gives the seed a great amount of buoyancy, in air as well as in water . The seed coat is derived from the outer integument and is made up of elongated cells with lignified walls . On maturing it loses its protoplasm thus appearing transparent . Only in a few primitive species like Apostasia , Selenipedium , Vanilla etc. the seed coat is highly sclerotic and opaque .

The ellipsoid embryo which is contained inside the seed coat have cells with dense protoplasm and several oil globules .

Due to lack of any nutritive tissue to make the germinating seed self-supporting , germination of the seed and further growth of the seedling in orchids is an extremely slow process . Contact with a suitable fungus under natural conditions or presence of a sugar containing medium, gives the seed the necessary stimulus for germination . The fungus digests the seed coat and the outer cell layers of the embryo enlarge , become cacuolate and the embryo assumes a spherical shape , pushing against the seed coat which stretches and is finally reptured . The cells of the embryo enlarge , become vacuolated and the embryo assumes a spherical shape, pushing against the seed coat which stretches and is finally ruptured . The cells of the embryo develop chlorophyll towards the tip and small papillae towards the base . This structure is now termed the protocorn. With further enlargement the apical portion of the protocorm. With further enlargement the apical portion of the protocorm differentiates into a meristamatic region which gives off the first leafprimordia . Within 4-6 months the first roots also appear . At the end of twelve months the seedling will be about 1 cm high with 6-7 leaves and 3-4 roots .

The description given above is the general pattern of germination of normal orchid seed under cultural conditions . What occurs in nature is essentially the same but an infinitely slower process. Since all orchids are heterotrophic at the seedling stage and have to depend upon the mycorrhizal fungus for their food supply , growth is slowed down to a considerable degree . The protocorn is heavily infected with fungus and as a rule , two or three years elapse before the first leaf appears above ground . Under artificial cultural conditions a seedling may reach flowering stage within 3-4 years . But in nature it takes anything from 8-16 years for a plant to produce its first crop of flowers . Summerhayes (1951) gives some exhaustive and pertinent data regarding this ovata , produces its first leaf in the fourth year but flowers only after 15 years . The burnt orchid, Orchis ustulata , remains in the protocorm stage for about 15 years depending entirely on mycorrhizal fungus for its nutrition. At the end of this period the first aerial shoot is produced as also the first tuber , after which the protocorm dies.

Among the epiphytic orchids , rate of growth may be a little faster than in the terrestrial species. Adderly (1970) reports that in Venezuela, where annual rainfall is between 100-150 inches, seedlings of Catasetum and Mormodes mature and flower within two years.