1226 A TEXTBOOK OF THEORETICAL BOTANY 



ment in such cases oblige us to recognize another mode of placentation, 

 namely median, apphed to ovules borne singly on the lip of the sill, although 

 he rejects Goebel's use of Celakovsky's term as being in a different sense 

 from that in which the latter author used it. It is not clear, however, 

 whether all solitary basal or pendulous ovules are, in fact, also median 

 in Troll's sense. 



These arguments and distinctions may strike the modern student 

 as savouring of scholasticism, but they sprang from a deep conviction 

 of the unity of the Angiosperms and a belief that there must be a funda- 

 mental uniformity in their reproductive structures, however varied its 

 expression might be. So multiform are the Angiosperms that any theory of 

 uniformity is certain to encounter difficulties, and suggestions of a diphy- 

 letic or polyphyletic origin of the group have frequently been made. 



It might be supposed that the former axial theory of ovulation would 

 have died out with the view that the ovule is a bud, but Sahni, from his 

 studies of Gymnospermae, came to the conclusion that there were two evolu- 

 tionary series among them; those in which the sporangia were axially borne 

 and those in which they were borne on sporophylls. These he termed Sta- 

 chyospermae and Phyllospermae respectively. This called in question the 

 view that all sporangia were associated with foliar organs. Recently Lam has 

 generaUzed this view and proposes to divide all cormophytic plants into 

 stachyosporous and phyllosporous series. Basing himself on Zimmermann's 

 telome theory, he holds that the stachyosporous condition, in which sporan- 

 gia are borne on axial structures, is the original condition and that the phyl- 

 losporous condition, in which sporangia are borne on a leaf which has 

 developed in one way or another from telomes, is relatively advanced. He 

 has extended his theory to include the Angiosperms and maintains that cer- 

 tain orders, e.g., Arales, Polygonales, Fagales, L^rticales and Euphorbiales, 

 are stachyosporous, while others, e.g., Ranales, Rosales, Guttiferales and 

 Liliales, are phyllosporous. The distinction is, in his opinion, an ancient one, 

 traceable to the beginnings of the Angiospermae in the late Jurassic. It cuts 

 across the differences between Dicotyledons and Monocotyledons and 

 implies at least two separate lines of ancestry from very early times. 



When we come to consider placentation in coenocarpous ovaries, we 

 find that it is divisible into two main types, called axile and parietal respec- 

 tively. Syncarpous ovaries are divided into loculi separated by septa, the 

 latter being regarded as the infolded side walls of the component carpels, 

 more or less completely fused to those of the neighbouring carpels on each 

 side, the number of loculi corresponding to the number of carpels; except 

 where " false septa " are developed, as in Lintim, Labiatae, etc., whereby 

 the loculi are subdivided and their number apparently increased. There 

 may even be horizontal septa secondarily formed, which produce two- 

 storied loculi. 



The carpel walls thus meet in the middle of the ovary, where they are 

 generally united together. The ovuliferous margins are, however, usually 

 recurved into the cavity of the loculus, where they develop unitedly or 



