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A TEXTBOOK OF THEORETICAL BOTANY 



carpels. This view was first advocated by Naudin in 1855 and it has attained 

 a wider following than any other, so that it has become almost axiomatic in 

 botanical teaching to say that the outer tissue of the apple, for example, is 

 receptacular and the core is carpellary! Goebel w^as largely responsible for 

 popularizing this view and his authority carried great weight. A variety 

 of this theory maintains that the placental region is axial (receptacular) 

 though admitting that the dorsal ovary wall is carpellary. (Fig. 1 1 1 1 , D & E.) 



4. Sachs in 1870 adhered to the second theory, above, but considered 

 that in some cases at least the central placentary region was carpellary, as 

 well as the top, in other words, that the carpellary portion of the inferior 

 ovary might be fertile as well as sterile. This is almost certainly true of 

 parietal placentae such as those in the Orchidaceae and may be true of some 

 axile placentae as well, the carpellary margins being supposed to be pro- 

 longed centripetally till they meet in the centre of the ovary. (Fig. 1 1 1 1, F.) 



5. The peculiar views of Gregoire on the unique character of the floral 

 axis led him naturally to the view that the inferior ovary is also a unique 

 organ with no parallel among vegetative organs. We have referred in more 

 detail to this view and the criticisms brought against it, earlier in this chapter. 



6. The " acarpous " theory, advocated by McLean Thompson in 1933, 

 which is really a development of the second or axial theory, combined with 

 some of the features of Gregoire's theory. The whole inferior ovary is inter- 

 preted as axial, produced by an excess of toral growth over apical growth, 

 leading to an invagination of the floral axis, within which megasporangia 



are borne. No carpellary or foliar structure is 

 supposed to take any part in its formation. 



Investigations have chiefly followed one 

 of two lines, either ontogeny, that is the 

 development of the floral primordia, or else 

 the comparative anatomy of mature flowers. 

 Most of the research has been carried out 

 under the influence of some theory and 

 strained interpretations have not been lacking, 

 but generally it may be said that ontogeny has 

 tended to support the axial theories and com- 

 parative anatomy to support the adnation 

 theories. In a few types, such as Rosa and 

 Calycanthits (Fig. 1 1 12), the vascular anatomy 

 suggests a double nature for the floral cup. 

 The vascular bundles from the stalk form an 

 outer ring in the cup, surrounding an inner 

 series of recurved bundles with a downward 

 course (and in Calycanthiis with reversed orientation) which supply the 

 ovules and are connected at a higher level to the exterior bundle ring. The 

 base of the cup, up to approximately the level of the bundle junctions, is 

 interpreted as axial, the ovary being definitely invaginated in a hollow recep- 

 tacle, while the upper portion of the cup is foliar. A few other examples 



Fig 



1 1 12. — Calycanthiis floiidits. 

 Longitudinal section of flower 

 with invaginated receptacle, 

 showing carpel traces with re- 

 versed orientation passing 

 downwards and inwards from 

 the axial bundles. {After 

 Smith.) 



