122 ON SEEDLINGS 



First pair ovate, obsoletely serrate, cuneate at the base. 



Second pair ovate, rather coarsely dentate-serrate. 



Third pair similar but more rounded at the base. 



Fourth pair unequal ; one leaf ovate, serrate ; the other tripartite 

 with ovate, serrate segments ; the lateral ones much the smallest. 



Ultimate leaves pinnatisect, with three to five or more segments ; 

 segments ovate, acuminate, coarsely serrate, opposite, the lower pair 

 generally stalked with or without two small segments on their basal 

 posterior side. Upper leaves tripartite ; uppermost undivided and 

 shortly stalked or sessile or reduced to bracts. 



Bidens humilis, H. B. K. 



Achene linear, very narrow, obtusely tetragonal with shallow 

 ridges and furrows between, glabrous, black ; two of the angles pre- 

 dominate and are produced into two horns surmounting the fruit. 



Seed linear, slightly broader than thick, conforming to the 

 interior of the achene, only falling short of the length of the 

 cavity ; testa thin, membranous, white or nearly so ; micropyle 

 and hilum contiguous, basal, inferior ; chalaza superior. 



Endosperm absent. 



Embryo comparatively large, filling the entire seed, straight, 

 colourless ; cotyledons linear, obtuse, entire, plano-convex, closely 

 applied face to face, lying in the broader plane of the seed with 

 their backs to the axis of the receptacle, narrowed somewhat towards 

 the base ; radicle terete, obtuse, slightly shorter than the cotyledons, 

 pointing to the base of the fruit but some distance above it. 



Receptacle somewhat concave, 3-3'5 mm. in diameter, bearing 

 forty to sixty achenes, of which thirty-five to fifty ripened in the 

 specimens examined. Achenes linear, slender, straight, 5-7 mm. 

 long, exclusive of the awns or teeth, -75 mm. wide, '5 mm. thick, 

 four-ribbed longitudinally. 



Seedling (fig. 465). 



Primary root long, flexuose, with numerous lateral rootlets, 

 annual. 



Hypocotyl erect, terete, glabrous, reddish, about 8 mm. long. 



Cotyledons linear, obtuse, subfleshy, flattened above with a sunk 

 midrib, convex beneath, broadest above the middle, amplexicaul 

 and connate at the base, attbut 1 cm. long, 1-1*25 mm. wide. 



Stem herbaceous, annual, erect, terete, densely covered with 

 hyaline, coarse, jointed hairs, and densely pubescent especially .when 

 young ; 1st internode 5'5 mm. long ; 2nd 9 mm. ; 3rd 1-1 cm. ; 4th 

 1-8 cm. ; 5th 4 cm. ; 6th 2'5 cm. 



