86 



PBAGTIGAL BOTANY. 



secondary roots spring from tlie upper parts of tlie stem, 

 or even from branches, they are called Aerial roots. 



CLASSIFICATION OF PKLMARY ROOTS. 



'from tlieir j perpendicular tap-roots (PI. I., 1-5). 



direction i. horizontal. 



very thin in proportion to their lenjrth, 



thread-like, ov filiform (PI. I., 1). 

 ''cross-sections orbicular, and all 



equal throughout cylindrical. 



cross-sections orbicular, gradually 

 thick decreasing in diameter down- 

 in pro- ward, and the vertical sections 

 por- lanceolate, as in Daucus Carota, 

 from their tion to spindle-shaped, or fusiform 



shape \ their -j (PI. I., 5). 



lenjifth, cross and vertical sections almost 

 and orbicular, and all nearly equal, 

 with globular. 



the cross sections orbicular, and ab- 

 ruptly decreasing in size down- 

 ward, .napiform, or turnip-shaped 

 (PI. I., 4). 



from their j not branching simple. 



branching ramose. 



hard and woody lignose. 



I. Simple pri- 

 mary roots, 

 which most 

 plants send 

 down from \ 

 the root -end ' 



. of the em- 

 bryo ; they 

 are called 



division 

 from their 

 consist- - 



soft and fleshy fleshy. 



II. Multiple primary roots — that is, several roots, which have sprung 

 all at once from the root-end of the embryo. They are also called 

 Fasicled roots. They are sometimes tuberous, as in Dahlia (see PI. I., 

 10). 



The absorbing surface of primary roots is sometimes 

 greater than it appears to be, since there are root-hairs, or 

 slender fibrils {Jihrillce), which abundantly cover the 

 younger parts of the root. These fibrils, when examined 

 with the microscope, are found to be slender tubes, which 

 imbibe the moisture around them. Slender, thread-like, 

 and freely branching roots are also called fibrous roots. 

 Roots are often tuber-like (tuberous), whether simple or 

 fascicled. Larger or smaller tuber-like excrescences form 



