186 MORPHOLOGY OF THE ANGIOSPERMS 



Whorled carpels represent modification of spiral arrangement. This 

 modification is often readily seen in internal structure where there is 

 little superficial evidence. 



The Terms Pistil and Locule. The term pistil is unfortunately loosely 

 used and confusing to students in its various morphological implica- 

 tions. It has been defined as the "unit of the gynoecium," but this "unit" 

 may be a single carpel — in apocarpous gynoecia — or a group of carpels 

 — in syncarpous gynoecia. The use of modifying adjectives — simple 

 where the gynoecium consists of a single carpel, and compound where 

 it consists of more than one carpel — are helpful, but "compound" is 

 sometimes used for both apocarpous and syncarpous gynoecia. "Pistil," 

 as a term applied to gynoecia, should be avoided as far as possible. 



The term locule is also loosely used, morphologically. It is applied 

 to the space enclosed within a single carpel, and to that within connate 

 carpels, both the common chamber and that within a ring of closed 

 carpels — Sempervimim, Phytolacca. 



Discussions of syncarpy and the inferior ovary conclude the discussion 

 of the carpel. 



THE CARPEL 



The angiosperm megasporophyll, the carpel, is, like the stamen, an 

 elongate appendage, primitively of laminar form. It is like the stamen 

 also in that it is leaflike in its relation to the stem — position, arrange- 

 ment, vascular connections (traces), anatomy, and ontogeny (apical 

 and marginal meristems). It differs from the microsporophyll in that 

 the megasporangia are always on the adaxial side, whereas the micro- 

 sporangia may be on either the adaxial or the abaxial side. In the 

 carpel, the sides of the lamina have been folded or rolled adaxially 

 toward the midrib. The folding or rolling encloses the megasporangia 

 (ovules) in a chamber, the locule. 



Form of the Carpel 



In its typical form, the carpel resembles a folded or rolled leaf 

 lamina, with margins usually appressed or fused. Ancestrally, it was 

 undoubtedly a stalked, dorsiventral organ. The folded organ is still in- 

 completely closed at pollination time in some taxa. Genera with the 

 stipe, a stalk, are frequent in both monocotyledons and dicotyledons — 

 Helobiales (Zannichellia, Scheiichzeria, Ruppia, Althenia); primitive 

 Liliaceae {Tofieldla, Veratrum); many woody Ranales {Dcgeneria, 

 Drimijs, Calycanthus, Bnbbia, some Annonaceae, Austrobaileya); many 

 Ranunculaceae {Coptis, Eranthis, Cimicifuga, Hellehorus, even some 

 achene-bearing genera, such as Thalictrum); Cercidiphyllum; Euptelea; 

 Faeonia; many Dilleniaceae; primitive Rosaceae (Physocarpiis) . The 



