The Science of Plant Growing 



39 



Fig. 23. Lily Scaly Bulb. Onion Tun icated Bulb 



as the cells of the ground tissue in that region thicken their walls greatly, 

 it follows that the outside of the stem of a Palm is very hard. A seedling- 

 remains without a stem till the leaves have attained a large size and a 

 certain number, when the stem rises up almost of the same thickness 

 throughout. As Palms generally do not branch or increase the number 

 of their leaves, the thickening 

 of the stem is unnecessary. 

 Some species of Dracaena 

 thicken their stems slightly by 

 some of the cells of the outside 

 of the ground tissue retaining 

 the power of dividing and form- 

 ing new tissue like the rest. 

 The stem of a Fern consists of 



ground tissue, with an inter- l W<V \U 



rupted ring of woody tissue in 

 the form of curved plates and 

 isolated pieces (fig. 22). In all 

 these cases strands of fibro- vas- 

 cular bundles pass from the wood of the stem or branches into the leaves. 



The functions of the stems and branches of all the above plants are to 

 support the leaves, so that they may be properly spread out to the light, 

 and to convey water and food to the leaves, flowers, and fruits. As the 

 stems of trees must be strong to bear the weight of branches and leaves, 

 so they develop a much larger proportion of woody 

 tissue than herbaceous plants require to do. 



Bulbs, Corms, Tubers, and Rhizomes. A bulb is 

 really a very much enlarged bud, consisting for the 

 most part of leaves, with a very short and thin flat 

 stem. Lilies have scaly bulbs (fig. 23), while Hyacinths, 

 Tulips, Daffodils, and Onions (fig. 23) have tunicated 



bulbs, so called because the sheaths 



are continuous all round, like a tunic. 



If the sheaths or scales are pulled off 



one by one there will remain a thin, 



solid part, which is the stem. The Tiger 



Lily, and several others, bear bulbils, or 



small bulbs in the axils of their leaves, 



and their structure is similar to the 



parent bulb. The bulbils form a ready 



means of propagating the plant (fig. 24). 



Conns are produced by the Crocus, Gladiolus, Colchicum (fig. 25) and 

 others. They consist of a short, flattened stem, covered with dry, scale- 

 like sheaths, or modified leaves, and surmounted by a tuft of perfectly 

 developed green leaves. They root from the base. They produce a new 

 conn, or several, on the top of the old one every year, the old one dying. 



Pig. 24. Bulb-bearing 

 Lily Portion of Stem 



Fig. 25. Colchicum 

 Corm 



