EMARGINATE COTYLEDONS 



43 



at the point where it articulates with the receptacle ; and the 

 cotyledons, which, with the rest of the embryo, eventually 

 occupy the whole interior of the seed, conform to this notch. 



In such cases as the Mustard (fig. 3), Cabbage, and Eadish, 

 the emargination is due to a totally different cause. The seed 

 (fig. 62, A) is oblong, thick, and slightly narrower at one end 

 than the other. There is no endosperm, so that the embryo 

 occupies the whole seed, and as this is somewhat deep, the 

 cotyledons, in order to occupy the whole space, are folded and 

 arranged one over the other, like two sheets of note-paper, as 

 shown in fig. 62, B-E, the radicle being folded along the edge. 



FIG. 84. Longitudinal and transverse sections 

 of seed of Cuphea silenoid.es, x 10 : oc, outer 

 coat ; ic, inner coat. 



FIG. 85. Achene of Nettle 

 (Urtica dioica), x 30: 

 J, testa. 



Fig. 62, D, represents the embryo a little opened out ; and 

 fig. 62, C, a section showing the radicle and the outer and inner 

 cotyledons. To this folding the emargination is due. If a piece 

 of paper be taken, folded on itself, cut into the form shown in 

 fig. 62, A, with the fold along the edge from ra to h, and then 

 unfolded, the reason for the form of the cotyledon becomes 

 clear at once. Zilla myagroides affords a similar case. 



But it may be said that in the Wallflower the seed has a 

 similar outline, and yet (fig. 86) the cotyledons are not 

 emarginate. The reason of this is that in the Wallflower 

 (Cheiranthus) (figs. 73, 74) the seed is more compressed than 

 in the Mustard and Radish (fig. 62, B, C), and the cotyledons 



