THE ANGIOSPERMAE 



1209 



pound ovaries the union is continued upward in the stylar region, the 

 individual styles being also united, but always marginally, surrounding a 

 central stylar canal which is never divided by septa. The placental tissue 



A B 



Fig. 1178. A, Papaver, transverse section of ovary with 

 elongated placentae forming false septa. B, Aieconopsis 

 with short parietal placentae. {After Le Maout and 

 Decdisiie.) 



is often continued upward into the stylar canal where, however, no ovules 

 are formed. It is possible that this upward extension of the carpel was once 

 part of the fertile ovary and that it has been sterilized for the advantage of 

 pollination, by elevating the stigma. If, then, the balance of growth were 

 to shift upward, so that the stylar region regained its fertility, while the 

 ovarial portion below was more or less suppressed, a paracarpous ovary 

 would result. Though the theory may sound rather far-fetched, it is sup- 

 ported by various facts, e.g., that paracarpous ovaries rarely, if ever, bear 

 stvles. Furthermore in some paracarpous ovaries, for example in Partiassia, 

 the base of the ovary is svncarpous. The biological function of the missing 

 styles may be produced either by the development of a gynophore {Cap- 

 paris), or by elongated stigmas [Dianthus), or by the elongation of the ovary 

 itself (Cruciferae). 



The interpretation of the single carpel as an infolded (conduplicate) 

 foliar structure is due to the theory of the flower propounded by Goethe 

 and adopted by A. P. de Candolle (1827) who wTote: " Each carpel may be 

 considered as a little leaf folded upon itself. " At that date it w'as permissible 

 to consider the carpellarv leaf as a " metamorphosis ", that is to say, a 

 purely ideal transformation of a " typical " foliage leaf, but the study of 

 evolution and particularly the study of fossil plants has taught us that there 

 can be no direct relationship between a carpel and a modern foliage leaf. 

 Each has, rather, evolved along independent lines from the primitive 

 branch appendages of the plants of a remote past, in which the distinction of 

 sterile and fertile appendages first become manifest. As Ozenda says, the 

 relationship is one of fraternity not of filiation. 



Both types of organ have retained some common features. They are 

 dorsiventral, they usually contain chlorophyll, both bear stomata on one or 

 both surfaces, and the carpel wall may contain a palisade tissue. They have 

 branching vein-systems and they may bear closely similar hairs or glands, 



