[Footnote 1: Gray's Lessons, p. 35, Fig. 86.]
[Illustration: FIG. 11.—1. Tap-root. 2. Multiple root of Pumpkin. 3. Napiform root of Turnip. 4. Spindle-shaped root of Radish. 5. Conical root of Carrot. 6. Aërial roots of Ivy.]
It is my experience that pupils always like classifying things under different heads, and it is a good exercise. The following table may be made of the roots they have studied, adding other examples. Dr. Gray says that ordinary roots may be roughly classed into fibrous and fleshy.[1] Thomé classes them as woody and fleshy.[2]
[Footnote 1: Gray's Lessons, p. 34.]
[Footnote 2: Text-book of Structural and Physiological Botany. Otto Thomé. Translated and edited by Alfred W. Bennett, New York. John Wiley and Sons. 1877. Page 75.]
| ROOTS. | |||
| Primary. | Secondary. | ||
| Fibrous. | Fleshy. | Roots of cuttings | |
| Aërial roots. | |||
| Sweet potatoes.[1] | |||
| Simple. | Multiple. | Simple. | |
| Morning Glory. | Pumpkin | Carrot. | |
| Sunflower. | Radish. | ||
| Pea. | Turnip. | ||
| Bean. | Beet. | ||
| Corn. | Corn. | ||
[Footnote 1: The Irish potato will very likely be mentioned as an example of a fleshy root. The teacher can say that this will be explained later.]
2. Fleshy Roots.—The scholars are already familiar with the storing of food for the seedling in or around the cotyledons, and will readily understand that these roots are storehouses of food for the plant. The Turnip, Carrot, and Beet are biennials; that is, their growth is continued through two seasons. In the first year, they make a vigorous growth of leaves alone, and the surplus food is carried to the root in the form of a syrup, and there stored, having been changed into starch, or something very similar. At the end of the first season, the root is filled with food, prepared for the next year, so that the plant can live on its reserve fund and devote its whole attention to flowering. These roots are often good food for animals. There are some plants that store their surplus food in their roots year after year, using up in each season the store of the former one, and forming new roots continually. The Sweet Potato is an example of this class. These are perennials. The food in perennials, however, is usually stored in stems, rather than in roots, as in trees. Annuals are generally fibrous-rooted, and the plant dies after its first year. The following experiment will serve as an illustration of the way in which the food stored in fleshy roots is utilized for growth.
Cut off the tapering end of a carrot and scoop out the inside of the larger half in the form of a vase, leaving about half of the flesh behind. Put strings through the upper rim, fill the carrot cup with water, and hang it up in a sunny window. Keep it constantly full of water. The leaf-buds below will put forth, and grow into leafy shoots, which, turning upwards, soon hide the vase in a green circle. This is because the dry, starchy food stored in the carrot becomes soft and soluble, and the supply of proper food and the warmth of the room make the leaf-buds able to grow. It is also a pretty illustration of the way in which stems always grow upward, even though there is enough light and air for them to grow straight downwards. Why this is so, we do not know.