Among all the plant groups, gymnosperms are among the most ancient seed-bearing vascular plants. Their ancestry can be traced back to the Mesozoic Era. They are important in terrestrial ecosystems and play a vital role in food chains. There are more than 1,000 species of gymnosperms. They include conifers such as pines and cycads. They are also important in paper sizing, soapmaking, and varnish making.
Gymnosperms have two types of reproductive structures, the male microstrobili and the female megasporangium. The male pollen is carried to the female cone by wind and insects. The female cones produce seeds. These seeds have a seed coat that arises from the integuments of the ovule.
The seed is composed of embryo, endosperm, and other tissue. The endosperm supplies nutrients to the embryo. The endosperm is derived from the mother plant and is rich in protein, oil, and starch. It is also a food source for young plants. In some gymnosperms, the endosperm is replaced by a cotyledon. Other gymnosperms have two cotyledons. The cotyledons are thick and leathery. They are shield shaped and may be one or two.
The ovule is an enclosing structure that stores nutrients in the seed. The seed is a product of a ripened ovule. In some species of gymnosperms, the seed is covered by cone scales.
Gymnosperms produce two kinds of spores: microspores and megaspores. The microspores are borne on the lower surfaces of the microsporophylls. The microsporangia undergo meiotic division to produce haploid microspores. They release reproductive spores that are released into the air.
Gymnosperms also produce reproductive spores that are released into a multicellular egg-containing structure called the archegonium. This structure ruptures when the pollen tube comes close. The tube grows towards the archegonium and the pollen grain settles on the surface. The tube is then digested through the megasporangium. In some gymnosperms, a pollen tube may also be digested by the archegonium.
Gymnosperms are among the most ancient and diverse seed-bearing vascular plants. They originated during the Mesozoic Era and are still important in terrestrial ecosystems.
Several seed-producing species, such as wheat, pea, and oats, are not albuminous. However, they do have a unique structure called a kernel. This is the point where food and other materials are stored. During germination, the seed coat protects the kernel from the elements while allowing water to enter. The seed coat also has a number of appendages, such as hairs, elaiosomes, and arils.
Seeds are composed of two main parts: the cotyledons and the seed coat. The cotyledons are simple structures that hinge together and contain a good amount of food matter. The seed coat is a tough, protective layer that reduces water content and provides a good surface for germinating seeds. The seed coat also has a number interesting functions.
In angiosperm plants, seeds are formed inside fruits. The most obvious function of the cotyledons is to store food. It also serves as a reservoir of essential nutrients for the embryo. It may enter a state of dormancy when it is not actively growing. The endosperm, on the other hand, is a food-laden tissue that acts as a food reserve for some monocots. It is oval, yellowish, and contains oil. In some dicots, the endosperm is the functional equivalent of a kernel.
The other, simpler function of the cotyledons was to carry the embryo. Embryos require oxygen to survive, and they can germinate if they are exposed to suitable conditions. They also need adequate moisture to survive. The endosperm serves to provide these essential nutrients. Embryos consume the endosperm as they grow. The endosperm is also the shortest link in the chain of fertilization. It is produced by fusion of male gametes with the secondary nucleus of a central cell.
Interestingly, non-albuminous seeds are also non-endospermic. The most obvious function of the cotyledons compared to the endosperm is to store food. However, this function is less obvious in non-endospermic seeds. The cotyledons also contain oil and starch.
There are a number of seeds that are considered to be non-endospermic, including pea, almond, grountnut, and Jack fruit.