To observe internal structures of different types of seeds.

Students dissect various bean seeds (that have been soaked overnight to loosen the seed coats) to examine their internal structure. Giant lima beans work especially well for this activity because the embryo can be seen easily without magnification. It is possible to remove the embryo from the giant lima without breaking it and actually watch the embryo grow on a water agar plate. Soaking a package of dried bean soup mix yields a variety of sizes, shapes, and colors for students to examine. The students can also open peanuts to find the small embryo inside. Children note similarities and differences between the internal structures of various types and sizes of seeds. The children are each given a giant lima bean seed to soak at home and then open for their families or plant.

When students first see the giant limas and are told that they will be opening them to see how accurate/inaccurate their initial seed diagrams might have been, they are curious about the size of these beans and why they have been soaked overnight. They accept the explanations that beans come in different sizes (Working with the assorted beans from a soup mix later in the lesson reinforces the idea that a wide range of sizes is possible for beans.) and that soaking the beans makes them easier to open.

Some students make a connection between the appearance of the soaked giant limas and what happened to the seeds in their germination bags. They observe that "water is making them lose their shell." The term seed coat is introduced. Young learners seem to link the work "coat" with the idea of protection. Several learners did include an outer layer in their early seed drawings and used text to explain that this layer's job is to protect the seed. Many more of the later seed drawings mention protection as the primary function of the seed coat.

While they are dissecting, several students mention that the large size of these giant limas is partially due to all of the water they soaked up. These students refer to the changes that took place with the seeds in their individual seed bags. It is important to show the class some of the dry giant limas so that they can make size comparisons between dry and soaked beans. Taking time to observe how the seed absorbs water, swells, and eventually splits the seed coat is important because many children who will readily and confidently state that a seed must have water to grow will struggle to give a good explanation for why a seed needs water. Their understanding of water's role in germination is limited to, "You water the seed and then it starts to grow." After observing, opening, and discussing the soaked seeds, many students are better able to articulate why seeds need water to start growing. These student comments show a range in understanding:

• " Water goes into the soil to the seed. The water give it something to drink and makes it powerful to break the seed."

• "Water could go in a hole and push the seed coat off. A dried seed is smaller."

• "Water makes the seed softer so the root can go out of the seed."

The idea that the seed is mostly food (for many of the seeds we studied) is surprising to students at first. One student compares the seed to an egg and explains that the yolk of an egg serves as food for the growing chick in the same way that the cotyledons are food for the "baby plant."

Students notice that the embryo has a root and distinct roots that they can identify. An embryo breaks off as the teacher is separating the cotyledons of a giant lima and this leads to great interest in whether the embryo can grow without its seed food supply. The embryo is placed on a water agar plate for observation. Over the next week or so, it does enlarge even though it is separated from the storage cotyledons.