Whenever you hear the term seed, you are likely to think of the seeds of a plant. However, there are other types of seeds. There are endosperm seeds and cotyledon seeds.
Endosperm
Several studies have focused on the structure of the endosperm of a seed during germination. The lateral endosperm contains four layers of cells at the periphery. The outermost cell wall is slightly thicker than the others. The cell walls of the inner layer are compressed.
The endosperm cap of seeds has been found to weaken during germination. This weakening may be caused by the presence of phytochrome-induced enzymes, which are known to weaken micropylar endosperm of Datura ferox L. It is not known if this activity is ABA-inhibited.
In order to study the occurrence of endosperm cap weakening, germination of tomato seeds was studied. Seeds were imbibed with water or ABA for 48 h. Wild-type seeds showed a decrease in required puncture force from 0.6 N to 0.35 N during the first 38 h of imbibition.
During the first 4 d of imbibition, gib1 mutant seeds showed no ice-crystal-induced porosity. The second step of weakening the endosperm cap may be cell separation.
Cotyledons
During the germination process of a seed, the cotyledon is the first leaf to appear. The cotyledon is a large shield-like structure and contains a radicle. The cotyledon also contains a plumule, which acts as a food reservoir and a source of nutrition.
The cotyledon has a life span of from a few days to a year. During this time, the cotyledon feeds the plant until its first true leaves emerge and take over food production. It will then wither and may yellow or dry up. In some cases, the cotyledon may even begin to become photosynthetic, which is one of the many reasons it is considered to be an important plant organ.
The cotyledon is part of the seed, so it contains a variety of specialized cells. Some of these cells will later become guard cells. Other cells may serve a short-term function in germination.
Cotyledons are also considered a good indicator of seed size because they are part of the seed. In many species, the number of cotyledons in a seed is a major feature in classifying the species. In some species, the number of cotyledons can be as high as twenty.
Dispersal methods
Various seed dispersal methods are used by plants to move, spread, and disperse their seeds. Some of these methods involve wind, fire, and water. Others involve animals, such as insects. These methods are important for the survival of plant species.
Fire is a very important seed dispersal method. Fire can cause plants to spread out, but it can also stunt the growth of newly dispersed seeds. This can be an issue in tropical forests.
Other types of seed dispersal methods involve the use of animals, such as birds and rodents. The seeds of these plants are covered with barbs and sticky mucous, which can hitch ride in the digestive system of these animals.
Some plants use feathers to hitchhike. This allows them to travel farther than seeds that use traditional methods of dispersal.
Some plants use spines to guide their seeds. Some of these spines are adhesive, meaning that the seeds will not fall off. Some plant seeds, like those in the pea, have seed pods that dry out when they are ripe.
Size of seeds found in the fossil record
During the Late Mesozoic, angiosperms diversified rapidly and radiated out of the tropics. However, they did not become large seeded until the Early Tertiary. The fossil record shows that most seed plants in the Early Tertiary had small to moderately small seeds.
These fossil seed plants represent adaptive radiation into an ecological niche space that was not yet occupied by any living species. Their size was also determined by their light environment. Seeds are generally larger in the central area of the pod.
Mesocyparis seed cones are ovate and 4.0-5.1 mm wide. The upper cone scales are larger than the basal cone scales. The position of the umbo has changed from the middle to the apex. The umbo is acute, and the seed cone is reflexed. The seed cones are borne in pairs.
The Rafflesiaceae family is known for producing seeds as small as 0.001 mg. They are also known for producing seeds as large as 27 kg. In addition to seeds, they produce flowers that have bracts that are decussate obovate, 3.7-4.3 mm long.
