Seed habit developed in extinct pteridosperm or Cycadofilicales. It is a group intermediate between cycads and ferns. The habit made the seed plant independent of the requirement of external source of water at the time of fertilizaton. in seedless vascular plants, the gametophyte must develop on moist soil with a thin sheet of water. The latter is required for the swimming of sperms for reaching the female sex organs.
As a result, seedless vascular plant could never become true land plants.They were popularly called as amphibian of plant kingdom

Cycas is called the 'relic of the past' It has following properties to justify this
i) Monoxylic wood through secondary growth started
ii) shedding of seed when embryo is still immature.
iii) The arrangement of microsporangia in all defined sori.
Phylogenetically, cycas is related to the pteridosperm (seed ferns) and through them to ferns from which it seems to have evolved. It can be ascertained by the presence of 
i) lead-like megasporophyll
ii) persistence of leaf base.

The vascular plants dominated land due to the following features (any two)
(i) Presence of deep, penetrating and widespread roots which anchor the plants and also absorb water and minerals.
(ii) Covering of aerial parts with waterproof material like cutin.
(iii) Mechanical tissues are present to allow them to rise to great heights.

Red algae The photosynthetic pigments located in the chromatophores are chlorophyll-a, d and \(\alpha \), \(\beta \) -carotenes, xanthophyll and biliproteins.
Green algae   Chromoplasts contain chlorophyll-a, b, carotene and xanthophyll.
Brown algae The chromatophores contain chlorophyll-a, c and \(\beta \),  \(\alpha \)-carotnes and xanthophyll.