442 



ON SEEDLINGS 



on each of its three faces ; testa thin, red, more or less adhering to 

 the suberous endocarp ; hilum and chalaza basal and inconspicuous. 

 Endosperm copious, floury, white when dry but yellow when 

 moist, surrounding the embryo except the radicle and sometimes the 

 edges of the cotyledons, appearing somewhat ruminated in transverse 

 section owing to the unequal thickening of the corky endocarp. 



Embryo straight, large, generally slightly excentric, colourless ; 

 cotyledons oblong, obtuse, entire, abruptly narrowed into the radicle, 

 lying near one side of the triangle in the transverse section of the 

 seed, and flat or slightly bent or doubled upon themselves longitudi- 

 nally ; radicle short, stout, narrowed to an obtuse point and lying 

 in the apex of the seed uncovered by the endosperm. 



Exceptions to the position of the cotyledons occur where one 

 is oblique to the other, often lying 

 against the sides of the seed from 

 the absorption of the endosperm 

 at their edges. A case occurred 

 where one cotyledon was twisted at 

 right angles to the other, so as to 

 occupy the three angles of the seed. 



Eheum officinale, Baill. (fig. 

 622). 



Primary root stout, fleshy, 

 tapering downwards, with lateral 

 fibres, brownish. 



Hypocotyl very short, fleshy, 

 brownish, hardly distinguishable 

 from the root, about 6 mm. long. 



Cotyledons broadly ovate, ob- 

 tuse, three- or obscurely five-nerved, 

 entire, scabrous at the margin, gla- 

 brous, fleshy, light opaque green ; 

 lamina 1-65 cm. long, 1-4 cm. 

 wide ; petioles flattened above, 

 convex on the back, pale green or 

 suffused with red, glabrous, connate 

 at the base forming a sheath for 

 the plumule, 1'75 cm. long includ- 

 ing the sheath. 



Stem herbaceous, forming a short, persistent, fleshy rootstock, 

 with large, fleshy, tuberous or tuber-like roots, elongating when about 

 to flower. 



FIG. 622. Rheum officinale, 

 Nat. size. 



