Tell what you have learned so far about primroses. What would you see if you could look inside the seed of a primrose? Today we will talk about germination, or what happens when seeds sprout. (Examine one of the diagrams at that link.)
When a seed falls into the ground, so long as the earth is cold and dry, it lies like a person in a trance, as if it were dead; but as soon as the warm, damp spring comes, and the busy little sun-waves pierce down into the earth, they wake up the plantlet and make it bestir itself. They agitate to and fro the particles of matter in this tiny body, and cause them to seek out for other particles to seize and join to themselves.Narration to follow here.
But these new particles cannot come in at the roots, for the seed has none; nor through the leaves, for they have not yet grown up; and so the plantlet begins by helping itself to the store of food laid up in the thick seed-leaves in which it is buried. Here it finds starch, oils, sugar, and substances called albuminoids. My note: This matter is a protein that is fibrous and insoluble in water, serving a protective or supportive function in the body; in other words, as well as being food for the new plant, it's also the stuff that holds the seed together, that gives it its shape.
This food is all ready for the plantlet to use, and it sucks it in, and works itself into a young plant with tiny roots at one end, and a growing shoot, with leaves, at the other.
Do you know what pith is? It often refers to the soft, spongy centre that you will find in some plant stems, such as young trees. Generally it just means soft, spongy tissue or plant material. When I was little, I remember being given an orange to eat and my parents telling me, "don't eat the pith." They meant the white stuff inside the peel and around each section of orange. By a strange coincidence, the next part of the lesson also requires an orange.
But how does it grow? What makes it become larger? To answer this you must look at the second thing I asked you to bring—a piece of orange. If you take the skin off a piece of orange, you will see inside a number of long-shaped transparent bags, full of juice. These we call cells, and the flesh of all plants and animals is made up of cells like these, only of various shapes. In the pith of elder (see photos) they are round, large, and easily seen; in the stalks of plants they are long, and lap over each other, so as to give the stalk strength to stand upright. Sometimes many cells growing one on the top of the other break into one tube and make vessels. But whether large or small, they are all bags growing one against the other. The cells of the seed are not empty; they are filled with something we call protoplasm, which is 90% water but which has a number of other important things in it as well.Narration to follow.
Now we are prepared to explain how our plant grows. Imagine the tiny primrose plantlet to be made up of cells filled with active living protoplasm, which drinks in starch and other food from the seed-leaves. In this way each cell will grow too full for its skin, and then the protoplasm divides into two parts and builds up a wall between them, and so one cell becomes two. Each of these two cells again breaks up into two more, and so the plant grows larger and larger, till by the time it has used up all the food in the seed-leaves, it has sent roots covered with fine hairs downwards into the earth, and a shoot with beginnings of leaves up into the air. Sometimes the seed-leaves themselves come above ground, as in the mustard-plant, and sometimes they are left empty behind, while the plantlet shoots through them.
How are your sprouting beans doing?
Something to think about: do you eat sunflower seeds or pumpkin seeds as a snack? Why does it make sense that they are high in protein?