THE ANGIOSPERIVIAE : STEMS 941 



5. Bulbs. \ bulb differs from a corm in that the stem is reduced to very 

 small dimensions and the body of the bulb is made up of thick, fleshy bulb- 

 scales. The difference is a question of proportion. In the corm the swollen 

 stem is the main storage organ and the scales are merely protective, while in 

 the bulb the scales themselves have been magnified and have replaced the 

 stem as the main storage organs. The stem is no more than a thick disc or 

 very flat cone, but it has an apical bud on the upper side, and adventitious 

 roots are formed in an annual crop from the marginal portion of the under- 

 side, their development following a resting period of from two to four months 

 after the conclusion of flowering. The fleshy scales are set very close together, 

 and their bases of insertion almost or completely surround the stem. In 



Fig. 929. — AntJwlyza panicidata. Group of attached 

 corms showing their sympodial branching. 



Tulipa the bulb scales are formed independently of the foliage leaves, but in 

 Narcissus they represent the persistent bases of the foliage leaves. In both 

 cases, however, they are richly stored with food material (Figs. 930 and 931). 



The bulb oi Lilium differs from the above examples, chiefly in the much 

 greater number and smaller size of its fleshy scales, the outermost being 

 loosely arranged and easily detachable (Fig. 932). In favourable conditions 

 these detached scales will produce adventitious roots and a bud which can 

 grow into a plant. 



The flowering bud for each year develops during the previous summer. 

 In Tulipa the apex of each bulb becomes transformed into a flowering axis, 

 but in Narcissus the apex itself persists and forms only a few foliage leaves, 

 the flowering axis being axillary. The branching of Tulipa is thus sympodial, 

 that of Narcissus is monopodial. 



The organs of the flower are completely formed in the flowering bud by 

 the end. of summer, together with the rudiments of the foliage leaves, and 



