STRUCTURE.] DECIDUOUS ROOTS. 239 



or lobed ; in the Dahlia, and many Lilyworts, they hang in 

 clusters, or are fasciculated. 



fig. 46. 



In internal structure the root differs little from the stem, 

 except in being much more fleshy or woody; its cellular 

 system, more especially, is subject to an unusually high degree 

 of development in such plants as the Parsnip, and other edible 

 roots. In Exogens, the mutual arrangement of the cellular 

 and vascular systems of the root and stem is of absolutely the 

 same nature. In many Endogens the roots are extremely 

 perishable, usually annual, and their woody bundles form an 

 imperfect hollow, or solid, cylinder, below the surface. 



In Water lilies roots are deciduous, and have a definite 

 position upon the rhizome, protruding from a cavity below 

 the surface, resembling an air-hole. Of this curious fact 

 the following account has been given by Munter : 



The entire surface of the rhizome of Nuphar lutea, the 

 Yellow Water Lily, is coated with leaf-scars directed obliquely 

 from above downwards, as in the stems of Cycads, and traces 

 of the torn bundles of woody fibre are left on these scars. 

 We do not, however, usually find any buds in the axils of the 

 leaf-scars. A little below the scars of the leaves, we find 

 single or grouped holes of the size of a pea, of a more or less 

 rounded form, which are either arranged beneath the leaf- 

 scars, or are only visible on those parts of the rhizome which 

 are turned towards the soil. When these holes are grouped, 

 three, five or six together, the lower ones are usually larger 

 than the upper, and on minutely examining them we find 

 a remarkable resemblance between each hole, and the 

 cavity of the human acetabulum. In the former a circular 



