嘉德麗雅蘭與蕙蘭種子發芽與芽的形成

Seed Germination and Shoot Formation of Cattleya and Cymbidium

蘭種子發芽之後有形成芽球（protocorm）與地下莖（rhizome）兩種。前者以嘉德麗雅蘭，後者以報歲蘭為材料，作詳細的掃瞄式電子顯微鏡的觀察。過去被認為嘉德麗雅蘭並無子葉產生的說法或許是錯誤的，而前人以為芽球體上的第一木葉可能是第三本葉之誤，在電子顯微鏡下可觀察到發育不完整的第一、二本葉。報歲蘭種子發芽的初期，與嘉德麗雅蘭很相似，只不過分化本葉的能力較差，只形成鱗片狀葉，緊貼在地下莖的分生組識上。地下莖在含有cytokinin的培養基上，第三日便發生很大的變化，而趨向莖葉的分化。前人所稱呼的蘭種子發芽時的毛狀物為假根（rhizoid），在電子顯微鏡下觀察的結果，較接近根毛（root hair）的形熊。

The in vitro morphological changes during seed germination of Cattleya and cymbidium, and the in vitro transforming of rhizome apex into shoot apex of cymbidium cv. Yuh-hwa were studied with light and scanning electron microscopes. During Cattleya seed germination, the globular embryos started to enlarge a few days after seeds been placed on modified Knudson C medium. Such enlargement was resulted from the increase in cell volume. The enlarging embryos eventually bursted open the seed coat longitudinally. By this time, the embryos developed into bipolar structures with stomatal apparatuses on the upper halves and groups of fins hairs on the lower halves of the embryo surfaces. SEM photos revealed that each hair was an outgrowth of a papilla protruding out from the outer wall of the epidermal cell, thus equivalenting to a root-hair. As the development continued, a circular protuberance appeared at the apical region enclosing the meristematic area. We suspected that this protuberance was the rudimentary cotyledon of Cattleya. The first and second leaf primordia, distichously arranged, subsequently developed. They were also remained in the rudimentary forms. The third leaf primordium appeared after five week's incubation. It developed into a tubulose leaf-the typical young leaf structure of the monocotyledonous plant. By this time, the embryo is generally referred as the ”protocorm” and is visible to the naked eyes. Protocorm formation and seedling development follow. The germination process of Cymbidium resembled to that of Gattleya except that rhizome is formed after germination and with weaker leaf development. Leaves assumed scale-shape and tightly covered the meristem of the rhizome. The apexs of rhizomes cultured in modified Knudson C medium would transform into well-developed shoot apexes in a ten-day-period when cytokinin was added to the culture medium. During such transformation, SEM revealed a gradual straightening of the curved scaly leaves. The flattened meristems gradually assumed conic-shape which in turn gave rise to normal leaf primordia.