(D) Seedlings

(1) Pines

Remove a pine seedling and examine the young root system, epicotyl, cotyledons, and ruptured seed  coat. Are any true leaves observable? With a dissecting microscope examine to see if there are buds for the first sets of true leaves. Compare this seedling with the embryo you observed in the seed. Is there any food reserve (megagametophyte) left?

(2) Beans and Peas

Compare the younger and older bean and pea seedlings. Note the ruptured seed coats, the cotyledons, the primary roots, epicotyl and first sets of true leaves. Compare the embryo of these species with  the seedlings as they emerge from the soil and in various stages of development. What structure emerges first from the germinating bean seed? What part of the shoot axis elongates most during the early stages of seedling development? Where does this place the cotyledons? What eventually happens to the cotyledons in beans? Compare this with the pea seedling. Do you notice anything different about the development of the pea and bean seedlings? What structure is represented by the bend of the shoot in the two seedlings?

(3) Grasses

Compare the corn or oat embryo with the seedlings in various stages of development. Identify the  primary and lateral root systems. Distinguish these from the adventitious roots arising from the cotyledonary node. What is the first structure to emerge from the germinating corn grain? What part of the shoot first emerges? Where is the shoot tip?

Consider all of these seedlings. Which shows the greatest initial growth rates, root or shoot systems? Describe what happens to cotyledons as the seedlings develop. What does it mean to say a seedling is established? How does water enter a seed prior to germination? Compare the thickness of the seed coat of pine with bean. Which is probably more impervious to water? Some seeds have extremely thick seed coats, that are completely impermeable to gases and water when first formed. What would have to happen to these seed coats for the seeds to germinate?