VEGETATIVE REPRODUCTION 159 
protecting sheath round the swollen stem. The old corm, 
drained of food, withers away, and the young one sinks 
down to occupy its place. The descent is assisted by the 
contraction of thick and fleshy roots (Fig. 63). In the 
autumn-crocus (Colchicum autumnale), which belongs to 
the Lily family, the new corm is formed at the side of the 
old one, and contractile roots are unnecessary. 
In large corms more than one corm is formed at the 
top of the old one, each of flowering size. In addition, 
a number of much smaller corms are formed as buds in 
the axils of the outer brown 
scales. These take a year or 
two before they have stored 
sufficient food to provide for 
flowers. Thus all the new 
corms are seated directly on 
the old one. This is not at all 
a good method, for they are so 
close together that some at 
least die through lack of food 
and air, brought about by over- 
crowding. Montbretia, a com- 
mon garden - plant, closely 
related to the crocus, has 
escaped this peril by producing 
a number of thin horizontal 
shoots, the tips of which swell 
out into new corms, often 
separated several inches from 5. 63 young Crocus 
the parent and from each other. Corm, wire Tack, FLESHY, 
4. Tubers (p. 110) are swollen ConTRACTILE Root (a). 
perennating organs, which, 
when detached, give rise to new plants. In_ the 
potato the tubers are stem structures containing a large 
quantity of starchy food -reserve, and bearing buds 
(‘‘ eyes’). When potatoes are planted, the eyes sprout 
and give rise to aerial shoots. A potato may be cut into 
pieces, and each portion will grow, provided it has an 
eye and sufficient reserve-food to give the new plant a 
start. In the lesser celandine the tubers are formed from 
axillary buds (p. 111). On the death of the parent the 
tubers become detached, and develop independently. In 
damp, shady places the lesser celandine develops long 
