The bulbs of Daffodils, Tulips, Snowdrops, Scillas, &c., all conform very closely to the Onion in structure. It will be noticed that at the base of the Hyacinth, for example, is a flattish or deltoid mass of tissue. This is called the "disc" and is really the stem portion of the bulb. On the upper surface it bears a number of thick scaly leaves packed very close together, and rolled round each other, with the flower-spike in the centre; while from the under surface, the roots emanate when growth takes place. It may be easily imagined by the reader that if the "disc" were drawn out lengthwise, and if a space separated one scale-leaf from another, that the bulb would be very similar in appearance to an ordinary leafy stem. Nature, however, has a certain object in view in modifying the stems and leaves in such a manner that they are tightly packed away when at rest, within a brown protecting coat, so that they resemble the large scale-protected flower-buds that may be seen in winter on Horse-chestnuts, Lilacs, Ash, &c. The thick scale-leaves are really storehouses in which food has been stored up by the larger and broader green leaves that perform the functions of assimilation, respiration, &c., above the ground during the growing period.
When the bulb begins to grow, the food in the thick scale-leaves is drawn up to supply nourishmentx to the flower-stem, until the new green leaves can manufacture or elaborate a fresh supply in the sunlight from the raw materials drafted into them from the soil by the roots. Under favourable circumstances more food is elaborated than is necessary for the wants of the plant, and then extra growths or young bulbs called "offsets" are developed at the base, or rather the side, of the older bulb.
It should be mentioned here, however, that all bulbs do not vegetate in the same way. In many cases the original bulb persists for several seasons, as in the Daffodil and Hyacinth, for example; but in others it vanishes completely during the period of growth, and is absorbed, or swallowed up, as it were, by the flower stem. The most common example of this among bulbs is the Tulip, to which more detailed reference has been made at [p. 133].
Kinds of Bulbs.—Most true bulbs are constructed like the Onion, Daffodil, Snowdrop, or Hyacinth, in having the scale-leaves rolled round each other, forming different layers or coats. Such bulbs are said to be "tunicated." In the case of the Liliums, however, the scale-leaves only lap over each other at the edges, and are arranged spirally round the central axis. These bulbs are called "scaly," or "imbricated," and are shown in the annexed sketch on [p. 12].
The individual scales are much thicker at the base than at the apex, and in the case of tunicated bulbs, they are also thicker on one side than the other. By this arrangement, the various "coats" can be rolled round each other more tightly, and without wasting any space.
Scaly Bulb of Lily.
[Definition of a "Corm.]"—In outward appearance, many corms are so much like bulbs, that the two terms are interchangeable and loosely applied, at least, among gardeners. By cutting a "corm" through the centre lengthwise, a great difference, however, will be noticed in the structure. In the bulb, the "disc" is small and unimportant, while the scale-leaves upon it are the most conspicuous feature. In the "corm," on the other hand, the "disc" is the all-important feature, and is devoid of any thick scale-leaves upon it. The new growths appear on the top or sides, and the lines round the circumference show where the sheathing papery scale-leaves were attached. In the "corm" then, it is the disc, and not the scale-leaves, that is the great storehouse of food.
PLATE 4.