OF THE OVARIUM OF SIPHONODON. 139 



are against this view, and when it may be imposSible to demonstrate it; and that 

 tliis law allows of no exception, — it seems natural to suppose that the law of the formation 

 of ovules in one of these whorls should be regarded as no less absolute, and that any 

 explanation that does no violence to nature should be accepted to account for apparent 

 exceptions, in preference to abandoning the general law and adopting a particular one for 

 those exceptions. Under this point of view I should prefer agreeing with those botanists 

 who consider that all placentation is axial, and that carpellary insertion is to be ex- 

 plained by supposing axes to be produced upon the carpellary leaves, rather than conclude 

 that nature resorts to two totally distinct and opposite principles in effecting the same 

 purpose with the same organs. The instances, however, of the ovules being normally 

 developed on the margin of the carpels, are so extremely numerous and convincing, and 

 the cases of insertion which are not at once reducible to this relation of parts are so 

 few and so scattered through different Natural Orders, that I cannot but regard the 

 latter as insufficient to invalidate the law in question, and to demand the operation 

 of another. 



EXPLANATION OF THE PLATE. 

 Tab. XXVI. 



Fig. 1. Flowering branch o{ Siphonodon celastrineus : — of the natural size, from Mr. Griffith's drawing. 

 Fig. 2. Bud at the earUest period of the appearance of the parts described : — of the natural size. 

 Fig. 3. Vertical section of ditto ; s. stamens. 



Fig. 4. Vertical section of upper portion of more advanced bud, the ovular cavities having just appeared. 

 Fig. 5. Another bud further advanced, the stigmata formed, and vascular cords to the ovules. 

 Fig. 6. Flower about to expand, cut vertically. The ovules are displaced, and the annulus swollen. 

 Fig. 7- Flower after impregnation, with the stamens stdl attached. 

 Fig. 8. Annulus from fig. 5, seen from above; t. the stigmatic teeth. 

 Fig. 9. Stamens seen from above, concealing the annulus. 



Fig. 10. Transverse section of annulus, showing the five stigmatic cords or passages. 

 Fig. 11. Portion of ditto much more highly magnified. 



Fig. 12. Portion of annulus, with stigma, conducting tissue, ovules, and vascular cords. 

 Fig. 13. Portion of another annulus with stigmata, an ovule and its vascular cord. 

 All but figs. 1 & 2 more or less highly magnified. 



t2 



