And now the plant can no longer afford to be idle and live on prepared food. It must work for itself. Until now it has been taking in the same kind of food that you and I do; for we too find many seeds very pleasant to eat and useful to nourish us. But now this store is exhausted. Upon what then is the plant to live? It is cleverer than we are in this, for while we cannot live unless we have food which has once been alive, plants can feed upon gases and water and mineral matter only. Think over the substances you can eat or drink, and you will find they are nearly all made of things which have been alive: meat, vegetables, bread, beer, wine, milk; all these are made from living matter, and though you do take in such things as water and salt, and even iron and phosphorus, these would be quite useless if you did not eat and drink prepared food which your body can work into living matter.Here's a science experiment for you to try. Take a glass of water, and put a straw in it. Put your mouth on the straw, but don't do anything else. How much of a drink did you get? Why didn't the water just come up through the straw? Of course you have to suck on the straw to make the water rise. Well, since plants can't suck water from the ground in that way, how can the water get up into the plant? Today we are going to do an experiment to show how osmosis works.
But the plant, as soon as it has roots and leaves, begins to make living matter out of matter that has never been alive. Through all the little hairs of its roots it sucks in water, and in this water are dissolved more or less of the salts of ammonia, phosphorus, sulphur, iron, lime, magnesia, and even silica, or flint. In all kinds of earth there is some iron, and we shall see presently that this is very important to the plant.
Suppose, then, that our primrose has begun to drink in water at its roots. How is it to get this water up into the stem and leaves, seeing that the whole plant is made of closed bags or cells? It does it in a very curious way, which you can prove for yourselves. Whenever two fluids, one thicker than the other, such as treacle (molasses, syrup) and water for example, are only separated by a skin or any porous substance, they will always mix, the thinner one oozing through the skin into the thicker one. This is called osmosis.At this point in the book, the teacher proposes an experiment involving a piece of bladder and some treacle, neither of which we have. However, The Little Giant Book of Science Experiments, by H.J. Press, suggests a similar experiment (“#253, Rising Sap”) that uses a carrot and other more easily obtainable supplies; you can read the directions on Google Books.
Now, the saps and juices of plants are thicker than water, so, directly the water enters the cells at the root it oozes up into the cells above, and mixes with the sap. Then the matter in those cells becomes thinner than in the cells above, so it too oozes up, and in this way cell by cell the water is pumped up into the leaves.Narration to follow ("explain osmosis").
You may also want to check out this article: "Osmosis Experiments with Gummy Bears."