30 The Nature and Origin of Stipules. 



together gives rise to such leaf-forms as are found in Vaccinium 

 and Sassafras, the principal portion of the lamina being formed 

 by the development of the apical portion, but including at the 

 base the lateral, central-basal and axial portions which are con- 

 tracted below into a short petiole. 



If we observe the development of the leaf in Sassafras the 

 relative growth of the several parts can be readily traced. The 

 first four leaves (fig. 1) are very simple. In the fifth (fig. 2) con- 

 siderable development has taken place. The apical portion, now 

 forming about half of the organ, is provided with the three typi- 

 cal veins as they appear in the adult leaf, but starting out sepa- 

 rately from the very base. The lateral portions have reached 

 their highest development and each is furnished with a pair of 

 veins. In the sixth leaf (fig. 3) there is a very close approach to 

 the adult form. The upper part has expanded and the lower parts 

 have elongated, removing the point of separation of the three 

 principal veins of the leaf to a considerable distance from the 

 stem. At the same time there has been a basal contraction look- 

 ing toward the formation of the petiole with a considerable de- 

 generation of the lateral portions, one of the veins having disap- 

 peared from each of them, while the other has become associated 

 with the midvein. The seventh leaf (fig. 4) represents the un- 

 lobed adult form and diff"ers but little from the sixth. 



A similar condition is observable in Ailayithus glandulosa Desf. 

 (figs. 5-10), but resulting in this case in the final separation of 

 the lateral portions as small gland-bearing fugacious stipules, com- 

 parable to those at the base of the leaves of many of the Ranun- 

 culacea. The comparison of Sassafras and Ailanthus shows how 

 small a difference in development may determine a leaf as stipu- 

 late or exstipulate. 



The case of Syringa vulgaris L. is like that of Sassafras, 

 though more difficult to trace, owing to the larger number of veins 

 in the leaf, but the homologies of parts may be followed more or 

 less distinctly from the second leaf up to the sixth, the first adult 

 leaf (figs. 11-14). The lateral portions are seen to have degen- 

 erated almost entirely and, their bundles having disappeared, they 

 remain onlj' in the margin of the petiole. 



The Compositse furnish examples of a similar course of develop- 

 ment but often with a closer approach to the true stipular condi- 

 tion, as the lateral portions are supplied with vascular tissue by 



