36 



PRACTICAL BOTANY. 



secondary roots spring from tlie upper parts of the stem, 

 or even from branches, they are called Aerial roots. 



CLASSIFICATION OF PEIMAET BOOTS. 



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



direction 1 /tonsoratoi. 



very thin in proportion to their lengtb, 



threadlike, ot 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, 

 tiou to spindle-shaped, or fusiform 



their j (PI. I., 5). 



length, cross and vertical sections almost 

 and orbicular, and all nearly equal, 

 with globidar. 



the cross sections orbicular, and ab- 

 ruptly decreasing in size down- 

 ward, .napiform, or turnip-sJiaped 

 (PI. I., 4). 



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 



from their 

 shape 



from their 

 division 



from their 

 consist- 



soft and 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 

 Fasided 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 {fibrilloe), 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 fhrous roots. 

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

 fascicled. Larger or smaller tuber-like excrescences form 



