TYPES AND KINDS OF STEMS 



43 



called " stemless " plants, and this is the meaning of acaulescent 

 plants. The plant appears to be composed only of root and 

 leaves. But there is a very short section of the stem, difficult to 

 define its limits, between the root and leaves and to which they are 

 attached. It is at the crown of the root, and for this reason such 

 a stem may be called a crown stem. Many biennials have crown 

 stems. The beet, turnip, parsnip and carrot are also examples, 

 but because of the large, fleshy root of these plants they are some- 

 times called crown tubers. The crown stem of the dandelion is 

 perennial and bears the foliage leaves. But each year it develops 

 one or more flower stems which die down after the seed ripens. 

 In the fleshy roots mentioned above, during the second year a 

 tall leafy stem is developed which bears flowers and seed. The 

 fleshy roots are reservoirs for the storage of food material (see 

 Chapter II). 



SPECIALIZED STEMS. 



73. Bulbs. A bulb is 

 a specialized shoot with a 

 very short stem which is 

 covered with numerous 

 overlapping thick leaves, 

 as in the onion, hyacinth, 

 lily, tulip, etc. The onion 

 is made up largely of 

 broad, thick, short, fleshy 

 leaves, or the leaf bases, 

 which overlap very closely 

 and make a more or less 

 flattened circular or oval 

 body. The outer leaves 

 are usually dead, thin, 

 papery and brown. A longitudinal section through the middle 

 shows well the thickness and relation of the leaves. At the lower 

 end can be seen the flattened very short stem to the upper surface 

 of which the leaves are attached, while the roots extend from the 



Fig. 44. 

 Section of onion "bulb," showing thick fleshy leaves. 



