Let us learn about Resemblance of Gymnosperms. After reading this article you will learn about: 1. Resemblances of Gymnosperms with Pteridophytes 2. Resemblances of Gymnosperms with Angiosperms.
Resemblances of Gymnosperms with Pteridophytes:
The gymnosperms and pteridophytes resemble each other as follows:
1. Both have independent sporophytes that are distinguished into root, stem and leaves.
2. The sporophytes possess a well developed vascular system.
3. The xylem in most of the members of both groups lacks vessels and the phloem lacks companion cells.
4. Many cycads resemble the ferns in having large compound leaves and in the circinate ptyxis of the leaves.
5. The alternation of generations is heterologous.
6. The female sex organs are archegonia both in pteridophytes and gymnosperms.
7. The male gametes of Cycads and Ginkgo are motile as in pteridophytes (ferns).
8. Many pteridophytes such as Marsilea, Salvinia, Azolla, isoetes, and Selaginella are heterosporous like gymnosperms.
9. Some of the heterosporous pteridophytes possess one megaspore in the mega-sporangium like gymnosperms.
10. The gametophytes of gymnosperms and heterosporous pteridophytes are endosporic.
11. The gametophytes are highly reduced. The male gametophytes of heterosporous pteridophytes and most of gymnosperms possess only two male prothallial cells.
12. The female prothallus develops before fertilisation and there is free nuclear division.
13. Development of a distinct embryo after fertilisation. The embryogeny is endoscopic in many pteridophytes and all gymnosperms.
14. Germination of spores is precocious in gymnosperms and hetersporous pteridophytes.
15. Dichotomous venation in Ginkgo and ferns.
16. Presence of megaphyllous leaves in both groups.
Resemblances of Gymnosperms with Angiosperms:
The gymnosperms and angiosperms resemble each other as follows:
1. Both include trees and shrubs which may be erect, scan-dent or climbing.
2. The root system is well developed and the roots may be diarch, triarch, tetrarch or polyarch. The roots possess secondary growth. The xylem is exarc in the roots.
3. The stem stele is eustelic. Secondary growth is found in the stem. The secondary wood may be monoxylic or polyxylic.
4. Both produce seeds.
5. Both groups are heterosporous and possess endosporic and reduced gametophytes.
6. The megaspore is in organic connection with the mega-sporangium and is never shed.
7. The nucellus is surrounded by an integument to form a structure called the ovule. The ovule has a micropyle and may be stalked or sessile.
8. The pollen grains grow into pollen tubes.
9. The male gametes are non-motile in majority of gymnosperms and all angiosperms.
10. The male gametophytes are highly reduced.
11. The germination of the spores is precocious.
12. The emberyogeny is endoscopic.