Tag: pictorial feature of plant kingdom

Angiosperms and Gymnosperms resemble each other in many characteristics on of which is the presence of ovule. The difference lies in the appearance of ovule, in Angiosperm the ovule is enclosed in ovary, whereas in Gymnosperms the ovule is naked. 

Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. Gymnosperms, like all vascular plants, have a sporophyte-dominant life cycle. The gametophyte is relatively short-lived. Two spore types, microspores and megaspores, are typically produced in pollen cones or ovulate cones, respectively. 

Zoodiogamy is a type of fertilization in plants, wherein the male gametes or antherozoids swim in a film of water to the female gametes present in the archegonium. This type of plant reproduction relates to evolution and  is found in lower gymnosperms besides algae, bryophytes and pteridophytes.

"Gymnosperms" include all seed plants other than the angiosperms, or flowering plants. The absence of an enclosing structure is believed to be primitive, thus the first seed plants were "gymnosperms. 

The term Spermatophyta refers to any of a group of higher plants, that produce seeds.  

Gymnosperms refers to the group of naked seed bearing vascular  plants. Their seeds are naked as these are not enclosed in an ovary, like that of the angiosperms. This group includes large trees, like the pines, conifers, cycads and Ginkgo. 

The "endosperm" is a tissue in which the nutrient substances necessary for the development of the embryo are deposited. In gymnosperms the endosperm is formed in the ovule during germination of the megaspore is a gametophytic tissue, which consequently becomes the female prothallus or the gametophyte with a haploid set of chromosomes. The archegonia in gymnosperms develop from certain cells of the endosperm.

In gymnosperms, below micropylar beak some of the cells of nucellus of ovule disintigerate to form pollen chamber.