286 MORPHOLOGY OF THE ANGIOSPERMS 



morphology and relationships of the higher plants more difficult, but 

 the obvious interpretation is often not the correct one. Recognition that 

 angiosperm sporogenous tissue is basically deeply sunken and lacks an 

 enclosing, protective wall opens new lines of search for ancestral forms. 



A critical interpretation of such obviously highly specialized organs 

 as the ovule and the anther sac has been retarded by expressions of the 

 viewpoint that structure should be accepted for what it seems to be in 

 the light of its location and apparent relationships. For example, state- 

 ments like the following are sometimes made: the ovules in free central 

 placentation are cauline, because they are borne on an apparent elonga- 

 tion of the receptacle; where congenital fusion has occurred and no 

 histological or ontogenetic evidence remains, as in many inferior ovaries, 

 the structure should be accepted as simple and not dissected into com- 

 ponent parts, no longer recognizable; "although an ovule is more than 

 a sporangium, as the ordinary anther is more than four sporangia, the 

 distinction is theoretical, rather than practical." (If only interpretations 

 where there is direct proof and those that are "practical" were under- 

 taken, morphology would make little progress. When critical detailed 

 comparisons of organ with organ in related taxa are not considered, 

 false interpretations, such as the presence of both foliar and cauline 

 ovules in the angiosperms, are made.) 



Cauline and Foliar Ovules — Stachyospory and Phyllospory. The posi- 

 tion of ovules — whether they are borne on stem or leaf — has been con- 

 troversial since the earliest days of morphological description. In the 

 eighteenth and often in the nineteenth centuries, all ovules were fre- 

 quently called cauline; in the twentieth century, interpretations have 

 been chiefly that all are foliar or some cauline and some foliar. The 

 interpretation that all are foliar has been said to be "interesting be- 

 cause of its ingenuity" of explanation. It can as well be said, when 

 ovules are generally accepted to be all foliar, that the explanations of 

 cauline nature for some ovules are remarkable for lack of ingenuity in 

 interpretation. When evidence from anatomy, ontogeny, and comparison 

 of flower and carpel structure in clearly related taxa is considered, all 

 ovules are foliar. The presence of stachyosporous and phyllosporous 

 ovules in different genera of the same family, even in different species 

 of a genus — Lychnis — can hardly be considered morphologically sound, 

 and these claims have been made only by those not experienced in 

 morphology. In all major vascular taxa, spore-bearing tissues are re- 

 stricted to morphologically similar parts of the plant body, not borne 

 indiscriminately on stem or leaf, as required by the stachyospory- 

 phyllospory theory. 



The angiosperm ovule need not be interpreted in terms of ovule 

 structure in other taxa; it is probably not a modification of the ovules of 

 any living gymnosperm and perhaps not of any known fossil taxon. If 



