LESSON 6.] SUBTERRANEAN FORMS : BTJLBS. 



45 



are usually upright, producing buds on their upper surface and 



roots from the lower. ' But (as we see in the Crocus here figured) 



buds may shoot from just above any of the faint cross lines or 



rings, which are the scars left by the death 



and decay of the sheathing bases of former 



leaves. That is, these are axillary buds. In 



these extraordinary (jupt as in ordinary) stems, 



the buds are either axillary or terminal. The 



whole mode of growth is just the same, only 



the corm does not increase in length faster 



than it does in thickness. After a few years 



some of the buds grow into new corms at the 



expense of the old one ; the young ones, taking 



the nourishment from the parent, and storing 



up a large part of it in their own tissue. 



When exhausted in this way, as well as by 



flowering, the old corm dies, and its shrivelled 



and decaying remains may be found at the side of or beneath the 



present generation, as we see in the Crocus (Fig. 71). 



107. The corm of a Crocus is commonly covered with a thin and 

 dry, scaly or fibrous husk, consisting of the dead remains of the bases 

 of former leaves. When this husk consists of many scales, there is 

 scarcely any distinction left between the corm and 



108. The Bulb. This is an extremely short subterranean stem; 

 usually much broader than high, producing roots from underneath, 

 and covered with leaves or the bases of leaves, 4n the form of thick- 

 ened scales. It is, therefore, the same as a corm, or solid bulb, only 

 it bears an abundance of leaves or scales, which make up the greater 

 part of its bulk. Or we may regard it as a bud, with thick and 

 fleshy scales. Compare a Lily-bulb (Fig. 73) with the strong scaly 

 buds of the Hickory and Horsechestnut (Fig. 48 and 49), and the 

 resemblance will be apparent enough. 



109. Bulbs serve the same purpose as tubers, rootstocks, or corms. 

 The main difference is, that in these the store of food for future 

 growth is deposited in the stem ; while in the bulb, the greater part 

 is deposited in the bases of the leaves, changing them into thick 

 scales, which closely overlap or enclose one another, because the 

 stem does not elongate enough to separate them. That the scales 



FIG. 71. Corm or siilid biilb nf a Crocus, 79. The Bamo, nit thrniigli lengthwise. 



