VEGETATIVE REPRODUCTION 



159 



-OL 



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 

 the parent and from each other. 

 4. Tubers (p. 110) are swollen 

 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 



FIG. 63. YOUNG CROCUS 

 CORM, WITH THICK, FLESHY, 

 CONTRACTILE ROOT (a). 



