臺灣海桐屬莖葉之解剖研究在生態上之含義

Anatomical Study of Leaf and Stem of Formosan Pittosporum, As An Ecological Implication

海桐科僅分布於舊世界，臺灣則僅產海桐屬，包括五種及一變種。分布自低海拔（海桐、七里香及蘭嶼海桐）經中海拔（部分疏果海桐）至高海拔（疏果海桐、細葉海桐及大葉海桐）。其中僅栽培之七里香，可成為小喬木者，餘為或高或矮之灌木，包括野生之七里香。於生育習性上，臺灣之海桐屬植物，均為中生習性稍偏於早生習性者。Carlquist（1977）介紹爭執性及中生型比值以指示導管受各種生態因子所發生反映情況。就整個海桐科植物而言，臺灣之海桐屬植物其爭執性比值與中生型比值均低，所有之高山種類均具有低的柵狀組織對細胞間隙之比值，但僅大葉海桐具有厚的角質層。因此高山種類低數值的爭執性與中生型比值，主要源於冬季高山常有凍霜之現象，因此引起值物體生理之乾旱。至於平地種類多具較厚之角質層，而此兩種比值的低數值，則起因於高溫，強光照及夏季常有長期乾旱的結果。研究臺灣產海桐屬植物莖解剖性質而獲得結論即同種海桐植物生於不同環境下，解剖性質不同，而不同種海桐植物生於相同環境下，具有類似解剖性質。

Pittosporaceae is exculsively native to the Old World. There is only one genus, Pittosporum, with five species and a variety in Taiwan. They are found from lowland (P. tobira, P. pentandrum and P. moluccanum), through median (P. illicioides in part) to high altitudes (P. illicioides in part, P. illicioides var. angustifolium and P. dophniphylloides). Except for the cultivated P. pentandrum which will grow into a small tree, most species of Formosan Pittosporum, including the wild P. pentandrum are small or large shrubs. They are all mesomorphic but more or less tend to be xeromorphic. Carlquist (1977) introduced vulnerability and mesomorphy ratios to indicate the reflection of vessel elements under various ecological conditions. In Pittosporaceae as a whole, both the vulnerability ratios and mesomorphy ration of Formosan Pittosporum are low. All alpine species, have low values of the ratio of palisade tissue to intercellular space; only P. daphniphylloides has a thick cuticle. Thus, the low figures of both ratios may reflect adaptation to a form of physiological drought, caused by the winter frost. For the lowland species, the thicker cuticle, the low figures for both ratios, may be by an adaptation to the high temperatures, sunny weather and long period of drought in summer. The study of anatomical characters of leaves and stems for Taiwan Pittosporum indicate that plants of the same species vary in anatomical characters when they grow in different environmemtal conditions, while different species, growing close together or under similar environments, have similar anatomical characters.