40 The Nature and Origin of Stipules. 



are plainly distinguishable, the petiole has begun its development 

 and the separation of the stipules has made considerable advance. 

 The ninth leaf (fig. 45) is well developed, with the large stipules 

 still showing considerable adnation. But in the tenth (fig. 46) 

 they are wholly free and much reduced, and higher up disappear 

 altogether. We could hardly have a more complete series in 

 illustration of the formation of stipules than this, giving as it does 

 all the stages from an extreme^ primitive leaf- form to that very 

 highly organized condition where the stipules have entirely dis- 

 appeared. By a comparison of the venation in the seventh and 

 ninth leaves, it will appear that the separate condition of the 

 stipules has been attained in the manner already described, partly 

 by the formation of an apical cleft, partly by the degeneration of 

 the central-basal portion bringing the base of the cleft lower down. 

 Meanwhile there has also been a considerable apical development 

 of the stipule itself. But this increase in size is lost again in the 

 tenth leaf and the reduction continues to final abortion. Meli- 

 lotus alba Lam. presents very similar though somewhat less 

 primitive conditions. 



While considering leguminous plants, a few words concerning 

 stipels, which are so characteristic of the family, would be in 

 place. They have been denominated as " the stipules of leaflets," 

 but I am convinced that the} T have no connection with stipules 

 whatever, but that they represent rudimentary leaflets which have 

 their origin in a tendency to increased compounding. The habit 

 has become so fixed in the Leguminosse that evidence of its ori- 

 gin is seldom met with. I have however seen, in Lespedeza capi- 

 tata Michx., one of the earliest leaves with the terminal leaflet 

 only developed and the two lateral ones represented by stipels. 



I have found more light on the question in other families where 

 the same tendency to increased compounding often occurs. In 

 Sanguisorba Canadensis L. (fig. 47) for example, very vigorous 

 plants sometimes show rudimentary leaflets, more developed in- 

 deed than typical stipels, but in the same position. Their char- 

 acter as leaflets of secondary rank is evinced by their occasional 

 removal to a little distance from the primary petiole. A more 

 striking case is that of Sumbucus Canadensis L. In this species 

 the leaves of young shoots springing up where the bushes have 

 been cleared away are frequently partially bicompound and there 

 are all gradations between the ordinary pinnate form and the 



