Seeds offer a powerhouse of nutrients. They are rich in protein, vitamins, minerals and dietary fiber.
On windy days, you might see dandelion seeds spinning around like helicopters. That is because seed dispersal is important to help plants reproduce. Seeds need to be scattered in places where they can get adequate sunlight, water and space for growth.
What is a seed?
Seeds are reproductive structures that disperse and can survive for long periods of time. They have three main parts: an embryo, endosperm and a seed coat.
The embryo is the result of a fertilization of an egg cell by two sperm cells. The endosperm is the nutritive tissue that is stored within the cotyledons of the embryo. The seed coat is made of maternal tissues and it protects the embryo.
In flowering plants, the ovaries of some flowers produce hard or fleshy fruits that enclose seeds. Other structures that enclose seeds include the fruit-like drupes of some shrubs and berries of some trees. Nuts are also a type of seed. Some gymnosperms do not form ovaries and therefore their seeds are exposed. These are often called “naked-seeded” plants.
Some seeds, such as those of the coco de mer palm tree, float in the ocean and help them disperse. Other seeds are attached to animal fur or feathers for dispersal by animals.
What is a seed’s function?
Seeds provide food to an embryo and a means for dispersal to a new location. They may be eaten by birds or rodents; carried away by water, wind or other currents; swept from a parent plant by mammals; or dispersed by their own mechanisms such as hooks and barbs that cling to fur or feathers or sticky hairs that stick to surfaces.
Many seeds have a hard seed coat that must be broken before they can imbibe (soak in) water. This is accomplished by scarification, which includes mechanical methods such as soaking in hot water or poking holes in the seed with a pin; and chemical methods such as treating seeds with chemicals that break down the coating.
A mature seed has a network of void spaces that allow for gas exchange between the outside air and its internal endosperm or embryo. This network is fine-tuned at the genetic and metabolic levels. Seeds come in a wide variety of shapes, from bean-shaped (reniform) to kidney-shaped — either square or oblong, all sides equal or longer than wider — and egg-shaped (ovate or obovate, broader below the middle). The embryo has one or two cotyledons or seed leaves (depending on whether it is a monocot or dicot) and a prospective shoot called the plumule.
What is a seed’s purpose?
Seeds serve to keep a species in existence until it is able to reproduce and form a new plant. Different mechanisms in seeds keep the embryo inside the seed alive until conditions are right for it to grow into an individual plant and replace the parent plant.
An outer covering called a seed coat protects the embryo inside. It also stores food, which is supplied by a substance called endosperm. This supply of food supports the embryo until it can sprout and start to make its own food.
Seeds come in a wide variety of shapes and sizes. They can be discoid (flat and elongated), ellipsoid, globose or subglobose (inflated but not fully round), lenticular or ovoid (inflated but not rounded), and reniform. They may be striped with parallel or longitudinal lines or ridges, oily like coconuts or yews, and have other appendages such as wings, a raphe, or caruncles (soft spongy outgrowths of the funiculus, as in corydalis). The surface of the seed coat may be smooth or roughened, wavy or retticular.
What is a seed’s role in nature?
Seeds are an important development in plant evolution. They allowed flowering plants (angiosperms) to spread and dominate biological niches on land, unlike mosses, ferns, and liverworts that reproduce using other means.
All fully developed seeds contain an embryo with stored food and a protective seed coat. When the embryo is alive and environmental conditions are right, the seed will “wake up” and grow into a full-sized plant (radicle, plumule, and leaves). This process is called germination.
Cecilia Zumajo, a graduate student in the New York Botanical Garden’s Pfizer Plant Research Laboratory, is studying how genes regulate seed development. In particular, she is interested in how seeds develop their pericarps, or seed coatings. Her work suggests that some of these structures evolved in response to environmental stresses, such as cold and drought. Other structures are adaptations for specific modes of dispersal. For example, hairs on some seeds help them travel by wind. Others have barbs or hooks that latch on to animal fur and feathers, or are carried away by water.
