The so-called bulb of the crocus is technically known as a corm (Fig. 56). It differs from a true bulb in consisting mainly of a fleshy, rounded stem in which the surplus food made by last year’s leaves is stored up. The plant is thus able to flower early, without waiting for the new leaves to supply food. The swollen stem bears one or more buds, and the whole is surrounded by tough tunics of scales. When the corm begins to grow, roots are put out from the base, and the [Pg 86] flowers and—later—the leaves of the buds expand. The foliage leaves continue their work after flowering, and the food which they make accumulates in the base of the former bud, which becomes swollen to form the new corm for next year’s flower. The leaves then die down, their bases becoming the tunics of the new corm. Fig. 56.—Crocus corm, seen from the side, from below, and in longitudinal section. c′, base of bud, which will grow into next year’s corm; fd.ch., food channel; flr, flower bud; l, young leaves; rts, roots; t₁, t₂, t₃, t₄, tunics. (× ½.) EXERCISES ON CHAPTER V. 1. Mention experiments, which prove that organic substances are formed in the leaves, and distributed to other parts of a green flowering plant. By what channels are they distributed? (1895) 2. Draw a cross section through the stem of a flowering plant selected by yourself. Explain the uses of the chief things seen in the section. (1897) 3. Mention experiments or observations which show by what tissues water ascends to the leaves, and nutritive substance descends from the leaves. (1897) 4. By what tissues does water pass along the stem of a tree to the leaves? Give proofs of your statements. (1898) 5. Describe the effect of a tight ligature upon a growing hazel stem. (1898) 6. What proofs can be given that the stem of a tree draws nourishment from the leaves? (1898) 7. Show, by describing and drawing one example, that the branch of a tree may preserve a record of past seasons in its wood. (1901) [Pg 87] 8. Mention an experiment which shows that organic substance formed in the leaves travels down the stem outside the cambium. (1901) 9. Obtain thin sections (e.g. plane-shavings) of as many different kinds of wood as possible, and gum them into a book, writing under each section the name of the wood and the direction (transverse, radial-longitudinal, or tangential-longitudinal) of the section. 10. Make yourself familiar with the appearance and characters of the different kinds of timber used in carpentry and joinery. 11. Notice the light-brown spots on the bark of twigs of apple and horse chestnut. These are called lenticels; they are breathing-pores. In how many other trees can you find lenticels? 12. Observe whether an ivy stem puts out roots only where they can become fixed to a support, or indiscriminately.