Plant Kingdom

Cycas belongs to Order Cycadales of gymnosperms because it has naked seed. It is not enclosed inside a fruit. It does not have double fertilization and so the endosperm formed is haploid in nature and not triploid. So it is not included in angiosperms as they have ovules (or seeds) produced inside fruit. This is the main difference between gymnosperms and angiosperms.

In green algae, the photosynthetic pigments are chlorophyll a & b, carotenes and xanthophylls. In phaeophyceae, the pigments are chlorophyll a, chlorophyll c and carotenes and xanthophylls. Phycoerythrin gives red colour to Rhodophyceae.

Gymnosperms are the most primitive seed plants. The plants are generally perennial, woody trees or shrubs. In general, tallest trees in gymnosperms, e.g., Sequoia sempervirens is 366 ft. in height. The male gametes of Cycas are largest (300 $\mu $) in size, they are visible to naked eye and are oval in form and top-shaped. The ovule of Cycas is also largest in the plant kingdom.

A fern plant body is sporophytic (2n) and is differentiated into roots, stems and leaves. On the ventral surface of leaves sporangia are borne in a group called sori. Inside the sporangium are present the spores which are formed by reduction division.

Thus the spores produced are haploid in nature and germinate to produce a prothallus that represents the gametophytic generation. Antheridium and archegonium are borne on this prothallus. Thus meiosis takes place at the stage of spore formation.