20 



MANUAL OF BOTANY 



Fig. 22. 



Forms of Boots. — The chief modifications of the forms of 

 the root depend upon whether or no the primary root persists, 

 and is always stronger than its branches ; or whether it is but 

 little developed and soon surpassed in vigour by the latter. In the 

 former case we have the tap-root and its modifications, the chief 

 of which are the conical, the fusiform, and the na^iform roots. 

 Conical Boo^.— When a tap-root is broad at its base, and 

 tapers towards the apex, it is termed conical. The roots of 

 Monkshood (Aconitum Napellus), Parsnip {Pastinaca sativa), 

 and Carrot {Dauctis Carota) (fig. 25) are familiar examples of 

 this form of root. Fusiform iJoot.— This term is applied to a 



tap-root which swells 

 out a little below its 

 base, and thence tapers 

 upwards and down- 

 wards {fig. 23). The 

 common Radish, and 

 Beet (Beta vulgaris), 

 may be taken as ex- 

 amples. Napiform 

 Root. — This name is 

 given to a root which 

 is much swollen at its 

 base, and tapers below 

 into a long, point, the 

 upper part being of a 

 somewhat globular 

 form (fig. 24). It 

 occurs in a variety of 

 the common Eadish 

 (which is hence called 

 the Turnip-radish), in the common Turnip, and in some other 

 plants. 



In the cases where there is no permanent primary or tap-root 

 we have other forms caused by modifications of the secondary 

 roots. When a root divides at once into a number of slender 

 branches or rootlets, or when the primary root is but little enlarged, 

 and gives off from its sides a multitude of similar branches, it is 

 called fibrous. Such roots occur frequently in annual plants, 

 and may be well seen in annual Grasses (fig. 30), and in bulbous 

 plants. Ti( bercular Boot. — When some of the divisions of a root 

 become enlarged so as to form more or less rounded, oval, or 

 ovoid expansions (fig. 26), the root is said to be tuherculated, or 



Fig. 22. The Mangi-ove-tree {Rhizophora Mangle). 



