CONSTANCE: SYSTEMATICS OF THE ANGIOSPERMS 427 



ternal stigmatic crests and two rows of ovules attached between and vascularized 

 by the midvein and the two lateral veins (Bailey and Smith; Bailey and Nast, 

 1943b, 1945a; Nast and Bailey, 1945, 1946; Bailey, 1949; Bailey and Swamy, 

 1951). It is remarked that, "the classical concept of an involute carpel with 

 marginal placentation and a localized apical stigmatic surface will have to ])e 

 modified" (Bailey and Swamy, 1951, p. 379), but the necessary emendation ap- 

 pears to be a relatively slight one, and the discovery has put the tenet of the 

 foliar homology of the carpel in an extremely enviable position (Just, 1952). 

 The biological significance of the enclosure of ovules has usually been re- 

 garded in terms of better protection of the ovules (Grant, 1950b; Mangenot, 

 1952) or of increasing the efficacy of insect pollination (Arbcr and Parkin, Rob- 

 ertson). However, Whitehouse has substituted an intriguing genetical hypothe- 

 sis (1950, p. 215) : 



It is suggested that multiple-allelomorpliic incompatibility of pollen and carpel tissue 

 has been the primary cause of the evolution of the closed carpel and of the success of 

 the angiosperms over their gymnospermous ancestors. The profound significance of the 

 closed carpel for angiosperm evolution would then lie in the protection of the ovules, 

 not from desiccation or the attacks of animals, but from fertilization by the individual's 

 own pollen, without appreciably restricting cross-fertilization. 



Phylogenetic trends in gynoecia from spiral to cyclic, from apocarpy to syn- 

 carpy, from numerous and indefinite parts to few and of mixed number, from 

 polyovulate to uniovulate, from superior to inferior, are generally acknowledged. 

 Reduction maj^ sometimes go beyond the bicarpellate stage, with degeneration 

 of one of the carpels (Wilkinson), or to a secondarily simple or "pseudomonom- 

 erous" condition (Eckhardt, 1937, 1938), or even to one approaching a gymno- 

 spermous appearance (Fagerlind, 1948). With syncarpy, further complications 

 and controversies arise. Saunders (1937-1939) believed that, on the basis of 

 vasculation, a syncarpous gynoecium was composed of two alternating whorls of 

 sterile and fertile carpels — her theory of carpel polymorphism, which has re- 

 ceived a great deal of discussion but won few adherents. Floral anatomy has 

 been used by Douglas (1944; cf. also Egler, 1951) to indicate that the outer tis- 

 sies of the inferior ovary are usually appendicular, as they appear to be in Be- 

 gonia (Gauthier, 1950), but Puri (1951, 1952a, 1952c) doubts that this prob- 

 lem is fully settled. Thompson has maintained that the inferior ovary is strictly 

 a receptacular, acarpous structure, and Leinfellner (1941) that it is axial exter- 

 nally, purely carpellary in the interior. In his interestihg quasiphysiological 

 discussion of the flower, Schaffner (1937) stressed three trends (which he be- 

 lieved to be orthogenetic) toward determinate growth, expansive growth result- 

 ing in the production of disks and hypanthia, and intercalary growth between 

 androecium and gynoecium. These developments are not, perhaps, very differ- 

 ent from those which Stebbins (1950) credits to allometry, comprising a shift 

 to zonal or toral growth, or from successive to simultaneous, developments which 

 have played such an important role in producing floral diversity. 



The importance of placentation for taxonomic purposes has been appreciated 

 since the time of Lindley, but there appears to be little agreement with regard 

 to it otherwise. In the latest review of the subject I have found, Puri (1952b), 

 emphasizing vasculation, recognizes some eight conditions of ovule attachment 

 in angiosperms. He apparently is inclined to regard the axile condition, in syn- 



