152 HERBS {BULBS, CO RMS, TUBERS) 
In many Liliaceae, e.g. onion or lily, and other plants, there is a 
modified shoot termed a bulb. It consists of a small disc-like stem at 
the base, bearing a more or less spherical mass of leaves above, these 
being closely folded over one another and swollen with reserves ; the 
leaves in an onion or hyacinth completely enwrap the bulb, which is 
said to be tunicated , whereas in the lily they merely overlap one another 
and the bulb is scaly. The outermost leaves of a tunicated bulb are 
usually thin, dry, and membranous, protecting the fleshy leaves. In 
the centre of the bulb the discoid stem is prolonged into the short 
inflorescence-axis. Roots are developed adventitiously from the lower 
side of the stem. It is evident that a bulb is simply a large bud with 
fleshy leaves. When it sprouts in spring or in the rainy season, it 
produces an inflorescence and some green leaves (borne on the same 
axis as the flowers, or springing from the tops of the bulb-leaves) at 
the expense of its reserves. After the seeding is over the leaves 
continue to assimilate, and new reserve-stores are formed, but not 
in the original bulb. In the axils of the leaves buds are formed, 
and into these the reserves are carried, and the buds gradually enlarge 
into ‘daughter-bulbs’ within the parent-bulb. Then when the latter 
dies down the new bulbs remain in its place. 
Another type of shoot is the corm or ‘solid bulb,* as seen in Crocus, 
Cyclamen, Colchicum, Eranthis, Bowiea, Testudinaria, &c. The lower 
part of the stem, at or below the level of the soil, is swollen out into a 
more or less spherical shape to contain reserve materials. At the top 
is the bud, which in the vegetative period forms the leafy shoot at the 
expense of the reserves. In many cases new corms are formed as 
branches on the old ones and the latter have usually only one year’s 
activity ; the branches may be on top of the old corm (Crocus) or at 
the side (Eranthis, Colchicum). In other cases (Bowiea, Hablitzia, 
Testudinaria, &c.), the corm is perennial, and a new leafy shoot arises 
each year from the top of it, usually in the axil of a leaf of the preceding 
year. The corm is often {e.g. in Crocus) covered outside by a few 
membranous leaves, so that it looks like a true bulb till cut in section. 
The corm is simply a variety of the stem-tuber. The name tuber is 
given to any swollen part of a plant in which reserves are stored up, 
except bulbs or leaves. The tuber may be of stem or root nature. In 
the former case it usually forms the termination of a special lateral 
branch, which grows out horizontally and swells up at the end. Under- 
ground tubers occur in potato (Solanum), artichoke (Helianthus), 
Ullucus, &c. ; they betray their stem nature by their axillary origin 
(p. 41), and by bearing leaves reduced to scales, in whose axils buds 
(‘eyes’) are formed. These tubers subserve vegetative reproduction; 
the connecting branches die away and the eyes sprout out into new 
plants at the expense of the reserves. The main stem forms tubers in 
the cases of corms already mentioned, and in Dioscorea, Basellaceae, 
Tamus, epiphytic Orchidaceae, &c. Roots swollen into tubers occur in 
Dahlia, Thladiantha, Dioscorea, Bravoa, Paeonia, Uragoga, &c. In 
Orchis and other terrestrial orchids a bud forms in the axil of one 
of the lowest leaves ; upon it is developed an adventitious root which 
grows into a tuber with the bud at its apex ; this hibernates and grows 
out next year into a new plant, and so on. In dandelion (Taraxacum), 
