Hydra 70
The spermaphytes , or spermatophytes ( Spermatophyta ), are the Plante S which produce Graine S.
The appearance of seed is a big step in the history of the evolution of the plants. One finds in seed all the condensed elements which allow the Bryophyte S and Ptéridophyte S to reproduce. Simply the elements of dissemination are not any more the spores resulting from the Sporophyte but directly the gamétophytes:
- gamétophyte male immature in the form of grain of pollen.
- gaméthophyte female carrying after fecundation an embryo, gamétophyte itself contained in the teguments of the mégasporange, the unit constituting a seed.
Among the spermaphytes, some have naked seeds (embryo surrounded of the Albumen and a fabric of protection): they are the Gymnosperme S with 4 current junctions.
Others, developing in more one double fertilization producing of additional feeder fabrics, protect their seeds inside the ovary which will give the fruit: they are the Angiosperme S with the junction of the Magnolophyta.
Reproductive cycles
Case of the gymnospermes
the haploid phase does not include/understand any more a free stage apart from the grain of pollen which corresponds to an immature male gamétophyte. the gamétophyte female develops entire on the sporophyte; both will form after fecundation a complex structure, the seed, which comprises fabrics of 3 origins.
compared to the Ptéridophytes for which the mobile phases were the spores and the
Anthérozoïde S (or Spermatozoïde S) one witnesses a slip of the mobile phases towards the immature male gamétophyte (grain of pollen) and towards a new entity which is the seed.
This part which corresponds to the sporophyte becomes the dominant generation under which the plant appears to us.
Case of the angiospermes
The haploîde generation starts with the formation of the ovules in the carpelles ones of the flower and the grains of pollen in cheesecloths. Its development is limited and occurs inside the flowers even if the phase of dispersion of the grains of pollen is sometimes spectacular.
The immature male gamétophyte (grain of pollen) germ on the mark, forms a pollen tube which transports 2 spermatic cores to the ovule. Whereas at the gymnospermes one of both fell through, here one observes a double fertilization, one giving the embryo, the other a gluten (triploid in the majority of the cases) by fusion of cores spermatic and 2 polar cores resulting from the gamétophyte female.
It is the dominant form of the cycle during which is done the chlorophyllian synthesis.
- purple: tri part or pentaploid following the cases
The seed is now included in a fruit which is thus a complex structure including/understanding of fabrics resulting from the 2 diploïdes generations, (spermoderme, périsperme, pericarp for the first), (embryo for the second), separated by a fabric coming from the 2nd fecundation, the albumem.
External bonds
Nds-nl: Zaodplaanten