Division Cycadeoidophyta : cycadeoids

The cycadeoids (all extinct) had vegetative features almost identical to those of cycads (Fig. ; Table ). The two groups differ only in subtle details of the differentiation of stomatal complexes and in leaf trace organization. On such characters alone, cycadeoids would never be considered distinct from cycads. However, cycadeoid reproductive struc­tures were quite different from those of cycads: Individual cones contained both micro- sporophylls and megasporophylls. Each ovule had a stalk, and the megasporangium was surrounded by an integument that extended out into a long micropyle. Between the ovules were thick, fleshy scales. Microsporophylls were located below the cluster of megasporophylls and curved upward, enveloping the megasporophylls. Each microsporophyll was cup-shaped and contained numerous microsporangia.

FIGURE :Vegetatively, the cycadeoids such as Cycadeoidea were very similar to cycads. Internally, like cycads, they had a broad pith, a small amount of parenchymatous xylem, a broad cortex, and a tough outer protective layer formed by persistent leaf bases.

مواضيع ذات صلة

البذور الاصطناعية Artificial Seeds

مقارنة بين نباتات مغطاة البذور (النباتات الزهرية) ومعراة البذور

مغطاة البذور (النباتات الزهرية) Division Mangnoliophyta

الصنوبـر (Pinus)

النباتات معراة البذور Gymnosperms

النباتات البذرية

بذرة الفول

بذرة الخروع Caster OiI Seed

حبة الذرة Zea mays

دراسة مثال لإنبات بذور ذوات الفلقة الواحدة

دراسة بعض الأمثلة لإنبات بذور ذوات الفلقتين

التغيرات التي تحدث للبذور أثناء الإنبات