3S0 



SIR J. LUBBOCK — PHYT0B10L0G1C\L OBSERYATIOXS. 



' In Selianthus Cucumis the seed itself is slightly notclied at the 

 polut where it articulates with the receptacle ; and the cotyle- 

 dons, which, with the rest of the embryo, eventually occupy the 

 wliole interior o£ the seed, conform to this notch. 



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

 emargination is due to a totally ditferent cause. The seed (fig. 74) 

 is oblong, thiclv, and slightly narrower atone end than the other. 

 There is no perisperm, so that the embryo occupies the whole 



Fig. 101. 



Fig. 100. 



rh. 



TTl 



K 



p 



Fig. 100. Longitudinal and transverse sections of C^ipjiea silenoides, X W. 



oc, outer coat of testa ; ic, inner coat of testa. 



Fig. 101. Achene of Nettle {Uriica dloica), x 30. J, testa. 



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 figs. 75-78, the 



7 represents the 



radicle heing folded along the edge. 



seed a little opened ont; and 



Fig. 



7 



fig. 



76 a section sliowing the 



radicle and the outer and inner cotyledons. To this folding the 

 emargination is due. If a piece of paper he taken, folded on 

 itself, cut into the form shown in fie;. 74, witli the fold along the 

 edge from m to /^, and then unfolded, the reason for the form ot 

 the cotyledon becomes clear at once. Zilla myayroides affords a 



similar case. 



But it may be said that in the Wallflow^er the seed has a similar 

 outline, and yet (fig. 102) the cotyledons are not emarginate. 

 The reason of this is tliat in the "Wallflower, Cheiranthis (figs- 

 90, 91), the seed is more compressed than in the Mustard and 

 Eadish (figs. 75, 70), and consequently the cotyledons are not 

 Folded; so tliat the whole, not the half, of each cotyledon 

 corresponds to the form of the seed. 



