THE CORM AND THE BULB OF PLANTS. 



71 



circulation of the plant. The precise mode in which the tuber enlarges is unknown 

 but it is quite clear that it must be freely supplied with circulating juices from the 

 stem. This is effected by the woody fibre, and bundles of it ramify within, the tuber, 

 and pass to each growing point. 



The structure of the tuber is very simple, being only a large mass of cells containing 

 starch, inclosed in a layer of condensed cells or cuticle. The woody fibre and other 

 structures bear no proportion whatever to the cellular tissue, and are not readily de- 

 tached. The cellular character is at once evident by placing a very thin slice of it under 

 the microscope, when a number of straight lines will be observed forming cells of much 

 regularity, and inclosing a large number of starch cells (Fig. 83). The starch may be 

 demonstrated by the addition of a watery solution of iodine whilst the section is uader 

 examination, when a beautiful violet colour will be instantly produced. 



This form of stem is also found in arrow-root, and has a more regular figure in the 

 asparagus potato. 



The Corm, as in the crocus, colchicum, 



and arum (Fig. 119), is a rounded, flattened, 



solid organ, bearing a bud upon its point or 



at its side, and leaves from its upper part. 



It is a compressed stem, and is restricted to 



monocotyledonous plants, and intervenes 



between the true roots and the reproductive 



buds. It usually contains much starch, 



accompanied by an acrid poisonous secretion, 



which militates against its employment as 



an article of food. 



The bulb, as of the onion and lily, is also 



an underground stem, or a stem in the rudimentary state of a 



leaf-bud. It is a fleshy, conical body, with scales surrounding 



Fifr. 119. The Cor- 

 mus of the ARUM 

 MACCLA.TUM, con- 

 taining starch. 



Fi. 120. A tuni- 

 cated bulb. with, 

 tern and roots. 



Fig. 121. 



A, naked bulb of LILY, showing its lateral stem and foliaceous covering. 



B, section of a bulb, showing its growing point at a. 



