FKOM SIMPLE LEAVES. 119 



But the most instructive foliage is that of the Honey-Locust 

 (Gleditchia triacanthos), Fig. 8. Among the highly cpmpound 

 leaves of this plant, the intermediate transitional forms be- 

 tween a pinnate, bipinnate, and tripinnate division of the 

 lamina may be readily found. We have had one of them 

 drawn. It will be seen, at a, that one side of the lamina of an 

 individual of one of the pairs of pinnae has developed three 

 new pinnules, and that two of them are only partially formed, 

 whilst the other side of the lamina retains its original appear- 

 ance. The individual which is thus nearly half-formed into 

 new pinnules differs hardly at all from the new pairs of pinnae 

 in size ; and the reader will perceive at once that these pin- 

 nules are five in number, and that this exactly corresponds 

 with the number of pairs of pinnules into which the terminal 

 and lower pairs of pinnae of the leaf have been developed. 

 Surely such proof as this makes it clear enough, that the 

 costa and side veins of a leaf may so develop that the former 

 shall become a common axis or support for the latter, which 

 shall constitute the midribs of new leaflets. 



Hitherto we have endeavored to prove that the irregularities 

 along the margin of leaves, described by the technical terms 

 serrate, crenate, dentate, etc., are to be attributed to an incipi- 

 ent effort at new leaflet-formation by the evidence of transi- 

 tional forms, a mode of reasoning which we think Naturalists 

 generally admit to be correct. But the same position may 

 be established by showing the intimate nature of that connec- 

 tion which subsists between the leaf and the other organs of 

 the plant, that it is only a . peculiar modification of the fibre 

 and parenchyma of the branch to which it is attached, and 

 governed by -the same general laws in its developmeDt. 



According to Dr. McCosh, the celebrated author of the 

 work entitled, " Typical Forms and Special Ends in Creation," 

 there is a correspondence between "stem ramification and 

 leaf ramification" in " the disposition and distribution of the 

 branches, and the disposition and distribution of the leaf 

 veins," and also " in the angle at which the branch goes off" 

 from the stem, " and that at which the lateral veins go off" 

 from the costa or midrib of the leaf. If this theory be true, 



