THE ANGIOSPERMAE 1223 



question. At most it can be said to place on those who believe in such an 

 emergence the onus of proving that it occurs. Fortunately, there are other 

 and more direct reasons for doubting it. First let us make clear that basal 

 or intercalary growth of appendages certainly does occur, and that the 

 basal growth of a whorl of coherent appendages will produce a cuplike 

 or tubular structure, as we have already pointed out in speaking of the 

 perianth. Furthermore, such a cup or tube may closely simulate a hollowed 

 axis, though it is morphologically a very different thing. To distinguish 

 the two structures may not always be possible, and it will, in any given case, 

 involve the application of all three methods of morphological inquirv, 

 namely, comparison, anatomy and ontogeny. Of these, ontogeny, although 

 the most direct, is perhaps the least trustworthy, owing to the difficulties of 

 the interpretation of embryonic appearances, but where it does give posi- 

 tive evidence it can be decisive. There may well be a residuum of cases in 

 which no available method will distinguish the two alternative hypotheses, 

 but we can generally establish a strong probability. 



The appendicular theory rests chiefly on anatomical evidence, about the 

 value of which opinions differ. Its negative findings are perhaps of little 

 consequence, but where, for example, the vascular structure offers positive 

 evidence of morphological changes, it is not to be lightly set aside, unless 

 we are prepared to believe that the course of vasculation is quite fortuitous 

 or that it can be easily and radically changed by physiological circumstances. 

 Against such assumptions stands the whole of stelar history, to be seen in 

 fossil and recent plants, which shows a surprising degree of conservatism 

 in vascular structure and that changes have come about by slow modifi- 

 cations of pre-existing structures, often lagging behind organismal changes, 

 rather than by wholesale rearrangements, abolitions and fresh creations. 



Van Tieghem based his view of epigyny on the departure of the trace- 

 bundles from the axial stele. He maintained that the position of departure 

 marked the true level of insertion of the appendages, which might be either 

 below or above their points of apparent insertion. If this were not so, he 

 argued, then the corolla tube of the Primrose must be regarded as axial in 

 the same way as the supposed axial cup of the inferior ovary. In some 

 flowers, as in Compositae, the separate trace-bundles of the floral appen- 

 dages can be followed throughout the ovarian wall and here there can be 

 little doubt of its appendicular character. In other flowers, as in Umbelli- 

 ferae, the vascular strands in the ovary wall divide into the individual appen- 

 dage traces only near the top of the ovary. The appendicular interpretation 

 of the latter condition would be doubtful were it not that Fames and his co- 

 workers have shown that all intermediate stages can be found, even within 

 the limits of a single genus, e.g., Vaccinium, thus demonstrating that there 

 is no essential difference between the extremes, and that the fusion of the 

 appendicular traces in the ovary wall does not make them any the less trace- 

 bundles. We may recollect the parallel case of the fusion of bundles in 

 epipetalous stamens. On the other hand recurved bundles, which turn 

 downwards from the system in the outer tissues to supply the carpels, have 



