1. A creeping stem.—Examine a plant of the ground ivy. Is the stem strong enough to stand upright? How does it spread out its leaves to the light and air? The stem grows along the ground, and at intervals it gives off a pair of leaves which grow upwards, and a tuft of roots which grow down to the ground.
2. A runner.—Is the “runner” of the strawberry of the same nature, i.e. is it a continuous stem like that of the ground ivy? When the plant is carefully examined, the creeping “stem” is seen to be a branch arising in the axil of a leaf. The branch runs along the ground for a little distance, and then roots itself and gives off a number of leaves. In the axil of one of these another branch arises and runs on in the same direction. The same branch does not run on and on.
3. A stolon.—Follow carefully the underground part of the couch grass and make out its connection with the main shoot. It is a branch like the runner of the strawberry, which arises in the axil of a leaf, and extends only to the next shoot.
Compare the stolons of the cinquefoil.
4. A potato tuber.—Examine a potato tuber (the part which is eaten). Notice the “eyes.” These are buds, with scale leaves. Leaves never occur on roots, so that the potato must be an underground stem. Put a pin into every eye, and wind a thread round the tuber along the bases of the pins. It forms a spiral. Cut the potato into halves, and pour a drop of iodine solution on the cut surface. What is the meaning of the blue dots which at once make their appearance? Plant a potato in warm, moist earth, and when it has sprouted notice that each bud (eye) has given rise to a branch.
5. Bulbs.—Cut an onion or snowdrop bulb down the middle, and draw what you see, marking on your drawing the outer scale leaves, the swollen bases of last year’s leaves, the young leaves in the middle, the short, thickened stem, and the roots. Also cut other bulbs across and again draw. What is the similarity and what is the difference between these bulbs and such a bud as a cabbage?
Also examine hyacinth, tulip and daffodil bulbs. Put them in glasses with water touching their bases, and watch them grow. What do they live upon?
6. A crocus corm.—Obtain a few crocus “bulbs” in the early winter. Observe the tough outer tunic springing round the edge of a circular scar on the base. If there are any roots they come off from the scar. Take off the tunics from one “bulb” and observe the bud or buds at the top of the white mass inside. Other tunics cover the buds. Cut lengthwise through the mass of the “bulb” so as to bisect the largest bud. Separate the parts of the bud with a needle and notice (a) the thin outer leaves, (b) the young foliage leaves, (c) the flower-sheath and flower. Pour a drop of iodine solution on the cut white mass (the stem) below the bud. It turns blue. Why?
What is the principal difference between a crocus “bulb” and the bulb of an onion, hyacinth, or tulip? A true bulb is mainly composed of swollen leaves or leaf bases; in the crocus the thick, rounded stem makes up most of the bulk. It is better, therefore, to speak of a crocus corm, to indicate the difference.
Plant the remaining corms and examine them at intervals for a year. Notice the formation of the roots, the lengthening of the buds, the formation of the flowers, the activity of the foliage leaves after flowering (why?), the withering of the roots and leaves in summer, and the growth of the enlarged base of the branch into next year’s corm.