Q.5 पत्ती की उत्पत्ति एवं विकास को समझाइए ।
Explain the origin and development of leef.
Answers
Answer:
In the shoot system of plants the leaf is the principal lateral appendage of stem. A leaf has determinate growth. The foliage leaves are of two types — microphyllous- and macrophyllous leaf and the leaves are also called microphyll and megaphyll respectively. The microphyllous leaf with a few exceptions has a single vein running from base to apex. The vein is not branched. In contrast the macrophyllous leaf has veins that are branched. The venation may be open and closed.
As regards phylogenetic origin there are two theories — Telome- and Enation theory. The former states that the leaves originated from telome trusses. A telome truss consists of telome and mesome. The ultimate dichotomy of fossil plants like Rhynia, Hornea etc. is called telome. The stalk that holds the telome or internode below the telome is called mesome. Telome and mesome together constitute telome truss.
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