THE BOOT, OR DESCENDING AXIS. 27 



128. The conical boot tapers its whole length, from the colluio 

 downwards (carrot). 



129. The napiform root, (turnip,) swells out in its upper part so 

 that its diameter equals or exceeds its length, as in Erigenia, Panax 

 trifolium (25, 25). 



34 80 31 82 83 



Fiaa. 80, Pffiony— flbro-tuberous roots. 81, Ginseng— fusiform root. 82, Pelargonium triste— 

 moniliform root, S3, Spirea filipendulo — noduloso root. 84, A creeping stem, ^vitli adventi- 

 tious roots. 



130. The forms op in axial roots are fibrous, fibro-tuberous, tu- 

 bercular, coraline, nodulous, moniliform, 



131. The fibrous root consists of numerous thread-lite divisions 

 sent off directly from the base of the stem, with no main or tap-root. 

 Such are the roots of most grasses, which multiply their fibres exces- 

 sively in Hght sandy soils. 



132. FiBRO-TUBEKOus ROOTS (or fasciculatc). Inaxial roots are so 

 called when some of the fibres are thick and fleshy, as in the asphodel, 

 crow-foot, pseony. Orchis, Dahlia. When the fibre is enlarged in cer- 

 tain parts only, it is noduloits, and when the enlargements occur at 

 regular intervals, it is moniliform (necklace-like). When it bears little 

 tubers here and there, as in squirrel-corn (Diclytra Canadensis), it is 



TUBERCULAR. 



133. Deposits of starch, or farinaceous matter, in all these cases, 

 constitute the thickening substance of the root, stored up for the future 

 use of the plant. 



134. Adventitious roots are such as originate in some part of the 

 ascending axis, — stem or branches, whether above or below the ground. 

 They are so called because their origin is indeterminate, both in place 

 and time. Examples are seen in the ground-ivy, twin-flower, and other 

 creeping plants. Several special forms should be noticed ; as, 



