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A TEXTBOOK OF THEORETICAL BOTANY 



most generally used for comparatively short, above-ground shoots which are 

 shorter than typical runners. As it has no precise significance it had better 

 perhaps be dropped. The same is true of the term sobole. 



2. Droppers, sometimes called Rhizomorphic Droppers. These are a 

 special kind of rhizomatous branch, produced from young bulbs (see below) 

 of Tulip, etc. An axillar}^ growing point is covered in by the inrolling over 

 it of a leaf initial, so that it lies inside a hollow hood comparable to a coleoptile. 

 The base of the leaf and the stem immediately below the growing point then 



6u/5 



Dropper 



Fig. 922. — Tulipa vitellina. 

 Garden hybrid. Bulb 

 bearing a dropper branch. 



Fig. 923. — Stachys tnherifera. Tuberous rhizome. 

 {From Vilniorin, " Les Plantes Comestibles.") 



elongate greatly, carrying the protected apex outwards and downwards from 

 the parent bulb, the base of the rolled leaf acting as a boring point, until a 

 suitable depth is reached, at which the enclosed growing point may develop 

 into a new bulb (Fig. 922). 



3. Tubers. These are solid, thickened stems or branches serving for 

 storage and also, if detached, for vegetative propagation. They may be 

 formed on rhizomes, on axillary branches or on main stems, either below or 

 above ground. Rhizome tubers are only distinguishable as such when formed 

 on comparatively slender rhizomes, such as those of Circaea, since swollen 

 rhizomes such as those oi Iris germanica may be regarded as tuberous through- 

 out. In Circaea lutetiana and in Cyperiis esculentiis the tubers are terminal 

 on rhizome branches. They contain the terminal bud, protected by scale 



