Take a well-grown straight seedling and measure off along its stem and along its root, beginning from the tip, distances 1 or 2 mm. apart, marking them with a fine brush and waterproof ink. Take care not to injure the plant, and also not to make the mark blurred or too big. Draw the plant showing the marks on it as accurately as you can, and make the drawing exactly life-size. Grow it in damp, but very loose sawdust, so as not to rub off the marks, and after one or two days take it out and compare it with your original drawing. You will find that the whole plant is bigger than when you first drew it. Look carefully at the marks on root and stem, and you will find that they are not all the same distance apart, as they should be if the plant had grown equally all over. The marks which are widest apart are those just behind the tip of the root and below the top of the stem, thus showing that there has been much more growth in these two regions than in the rest of the stem or root (~see~ fig. 28). If you repeat this often with many plants you will find that these are the actively growing parts of the stems and roots; the individual leaves, of course, are also growing. Thus we see that ~growth is not a simple stretching of the whole, but that there are two definite regions~ where it is specially active. That of the stem and first root carry on the growth in opposite directions, as we noticed before (~see~ p. 11), the normal stem growing up into the air and the root down into the soil. [Illustration: Fig. 29. A, Bean seedling planted upside down. The root has bent right over and is growing vertically down. B, later stage of the same. The shoot has bent up.] You can see ~how very determined the directions of growth are~ by planting upside down a bean which is just beginning to sprout, so that its root points up into the air. As it grows you will see the root bending over till it points vertically downwards, while the stem bends up and grows straight into the air (~see~ fig. 29). The same thing happens if you plant a seedling on its side, and even if you take quite a big seedling, which has grown in the usual way, and then place it upside down in moist air, you will see the root and shoot bending in order to get into their right positions. This very determined growth on the part of roots and stems seems to show us that they must have some means of “perceiving” and regulating their position. It is not an accident that they always grow in these very definite directions. Let us find out what we can about this question. Take a seedling and mark its root as you marked the roots for the experiment on the region of growth (~see~ fig. 28), lay this seedling on its side on soft, damp sawdust, so that the root can easily bend into it. Next day you should find that the end of the root has bent, and that the bend is in just about the same region as that which showed the most active growth.