12 BUDS AND STIPULES 



a sheet of notepaper, and one lies inside the other. 

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

 paper betaken, folded on itself, cut into the form shown 

 in fig. 12. with the fold along the edge from m to //, 

 and then unfolded, the reason for the form of the coty- 

 ledons becomes clear at once. 



Now let us test this ex- 

 planation by another case. The 

 Wallflower has a seed of similar 

 shape to that of the Radish, 

 though thinner. Now, are the 

 cotyledons of the same form 

 as in the Mustard or Radish ? 

 Not at all. Those of the Mus- 

 tard, as we have seen, are kid- 

 ney-shaped ; those of the Wall- 

 flower are racket-shaped, as in 



fig. 15. At first this seems a 

 Fig. 15. Seedling of Wall- 



flower. Two thirds nat. difficulty ; but on looking closer 



the difficulty vanishes, for while 



the cotyledons of the Mustard are folded, this is not the 



case with those of the Wallflower, which lie flat in, and 



conform to the shape of, the seed, as shown in fig. 16. 



Thus the difference, which at first sight seemed a 



difficulty, is really a confirmation of the explanation 



suggested. 



But we may even carry the matter a step farther. 



Why are the cotyledons of the Radish folded, and not 



