STEMS AND THEIR VARIETIES 59 



the end of summer, the green parts of the leaves die and shrivel ; 

 their lower parts, which have become thin, act as a co^er for the 

 rest of the bulb, and prevent the rapid loss of water from the 

 interior. 



The onion bulb, if planted next year, forms adventitious roots 

 from the base of the stem, and the terminal growing-point (/) 

 inside grows up into the air, and produces leaves and an inflor- 

 escence of white flowers at the end of a long hollow stem. The 

 buds in the axils of the scale leaves develop usually in the same 

 manner, so that from one bulb several flowering shoots are often 

 produced. The materials stored in the bulb-scales are used up 

 in this development of the flowering stems, and after the pro- 

 duction of ripe seeds, the whole plant is generally exhausted, 

 and dies away, in which case the onion is a biennial plant. 

 Occasionally, however, some of the lateral buds from the axils of 

 the scales do not produce inflorescences, but leafy shoots only, 

 which form small bulbs in the same manner as an onion seedling. 

 After the death of the parent, these smaller bulbs remain, and 

 carry on the growth in the succeeding year. The onion plant 

 in this instance is a perennial. 



A tulip bulb in autumn consists of a short, thick stem, upon 

 which are placed a series of large, overlapping, fleshy scales. 

 The latter are complete leaves, and not merely leaf bases, as 

 in the onion. At the apex of the stem is an embryonic shoot, 

 having leaves upon it, and bearing a terminal flower ; in the 

 axils of some of the scales are rudimentary buds. 



In spring the flower-bearing stem grows from within the bulb 

 and comes above ground, carrying with it the flower and two 

 or three leaves, as indicated in Fig. 25. This development 

 takes place at the expense of the food stored in the scales {0) : 

 the latter therefore soon become s_oft, and at the end of the 

 season shrivel up and decay. The leaves (e) on emerging 

 from the soil turn green, and during the spring and summer 

 manufacture a considerable amount of food ; that part of it 



