i8o THE STRUCTURE OF ECONOMIC PLANTS 



The Shoot. — The plant has a biennial habit, although it may 

 persist vegetatively as a perennial by means of bulbs. The sub- 

 terranean stem is a short, subconical structure from which the 

 linear leaves are diverged in a |^ phyllotaxy. It produces a long, 

 hollow, leafless stem which arises from the terminal bud of the 



Fig. 8i. Basal portion of onion showing the bulb, the two-ranked arrangement of leaves, 

 the manner in which the leaf sheaths enclose younger leaves, and the adventitious roots. 

 (Photograph by J. Horace McFarland Co.) 



underground axis and bears the inflorescence at its apex. In some 

 instances, lateral buds from the axils of the fleshy leaves of the bulb 

 may develop into flower stalks and produce terminal inflorescences. 

 The leaves arise from the short crown stem in a compact series, 

 and the sheaths of the outermost, older leaves enclose the younger 

 ones. The sheathing base of each leaf completely encircles the 

 stem, and it is the development of the fleshy leaf bases, together 

 with the absence of internodal elongation, that results in the for- 



