SECTIONAL TRANSACTIONS.— K. 383 



Afternoon. 

 Visit to Weetwood Hall. 



Saturday, September 3. 



Excursion to Bolton Woods. 



Sunday, September 4. 



Excursion to Malham. 



Monday, September 5. 

 Discussion on the Carpel. 

 Miss E. R. Saunders. — 



In the hitherto generally accepted interpretation of the Angiosperm gyncecium, 

 only one type of carpel is recognised. This is conceived as a leaf member, folded 

 inwards so that it becomes united either along its own margins or with those of its 

 neighbours, and capable of bearing on these sutures from one to several rows of ovules. 

 This conception is based mainly on the gross anatomical appearances in the earliest 

 stages of flower development and on the outward aspect of the mature ovary. Neither 

 method of examination is sufficiently refined to furnish critical evidence. Further- 

 more, certain features in some ovaries can only be brought into line with this 

 monomorphic view by distorting the facts. Exceptional cases in which the carpels 

 take on a leafy character have also been cited in support, but here, too, it appears 

 that the evidence ha« often been misinterpreted. 



The monomorphic view entails the acceptance of many morphological incon- 

 sistencies and unfounded assumptions. Among these may be mentioned the com- 

 missural stigma, the solitary terminal carpel, free-central placentation, false partitions, 

 supernumerary styles and stigmas. It offers no explanation of the obdiplostemenous 

 condition, of the occurrence of dimorphic fruits, of reversed orientation in allied forms 

 or of certain modes of fruit dehiscence. In innumerable cases it is at variance with 

 the clear evidence afforded by the vascular system and the stigma form, which has 

 been almost entirely ignored. 



On the other hand, the conception of the carpels as polymorphic structures offers a 

 satisfactory explanation of all the above features, and accounts besides for many 

 minor anatomical characters which, on the monomorphic interpretation, appear to 

 be without significance. On this view it is held that two main carpellary types have 

 originated in the course of evolution, the valve (hollow) type which, so far as appears, 

 never bears more than a single row of ovules on each margin, and the consolidated (solid 

 and semi-solid) type in which from one to several rows of ovules may be borne on either 

 ■side of the midrib. With this diversity in carpel form there very generally occurs 

 a redistribution of the three carpellary functions (stigmatic, protective, reproductive). 

 When two types of carpel are present in the ovary, one only, as a rule, is fertile. The 

 stigmatic function may similarly be restricted to one or other type, or may be per- 

 formed by both. This polymorphic condition is found to occur throughout the whole 

 range of Dicotyledons and Monocotyledons. 



Dr. H. Hamshaw Thomas. — 



When a morphologist who has been mainly occupied with the Pteridophyta turns 

 to study the carpel he will be struck with the great neglect of anatomical evidence. 

 Prior to Miss Saunders's, the only general survey of the vascular supply of the carpel 

 ■was that of Van Tieghem, and he was concerned mainly with the demonstration of the 

 foliar nature of the carpel. He gave the Ranunculaeese, the Leguminosse and 

 Epimedium as examples of plants having simple carpels of the primitive type, but in 

 the light of recent work not one of these plants can be regarded as having carpels 

 composed of simple infolded leaves with marginal ovules. 



Most authors have cited the megasporophyll of Cycas as the type of structure 

 from which the closed Angiosperm carpel was evolved. This view is based only on 

 analogy. The ovary of Caytonia deserves as much, if not more, attention, even 

 without postulating any direct relationship between the Caytoniales and the flowering 



