CHAPTER II. THE ROOT. 



produces are small as compared with the main root ; in this case it 

 is called a tap-root. Fig. 3 represents the tap-root of the com- 

 mon Stock. Sometimes, however, the embryonic root almost 

 immediately breaks up into numerous similar branches, forming 

 multiple primary roots. These may become thickened and 

 tuberous, as in the Dahlia, Fig. 4, or they may remain slender 

 and fibrous, as in the roots of the Plantain. 



Not infrequently the primary root disappears altogether at 

 an early stage of the development of the plant, and is replaced 

 functionally by other roots springing out laterally from the stem 

 higher up. This is almost universally the case with the large 

 group of flowering-plants called Monocotyledons, typified by the 

 Lilies, Palms, Grasses and Sedges, and with the higher flowerless 

 plants, such as Ferns, Club-mosses and Horse-tails. Roots of 

 this character and all others which originate laterally from stems, 

 branches or leaves, whether above ground or beneath it, are 

 called adventitious roots. Such are the aerial roots of the Ivy, 

 illustrated in Fig. 1, the roots which spring from the branches 

 and above-ground stems of various species of the Fig, from the 

 joints of some grasses, and from the rhizomes or underground 

 stems of such plants as Podophyllum, Serpentaria and Iris. 



r 



Fig. 7. 



Fig. 8. 



Fig. 5. 



Fig. 5. — Fusiform root of the Radish. 

 Fig. 6. — Xapiform root of the Turnip. 



Fig. 7. — Xodose roots of the Dropwort. 

 Fig. 8. — Fibrous roots of a Grass. 



It is often convenient to describe roots by their shapes. That 

 of the Carrot, which is thick at the base and tapers gradually to 

 the apex, is called conical ; one which is shaped like the root of 

 the Radish, Fig. 5, is called fusiform ; one shaped like that of 

 the Turnip, Fig. 6, tiapiform ; roots like those of the Dropwort, 

 Fig. 7, nodose ; roots like those of the Sweet-potato and Dahlia, 



