216 



FORMATION OF THE PLACENTA. 



out its organogeny (6'pyctvov, organ, and yivioig, production or develop- 

 ment) separate and axile. 



443. This placentation, therefore, has been accounted for in two 

 ways, either by supposing that the placentas in the early state were 

 formed on the margins of carpellary leaves, and that in the progress of 

 development these leaves separated from them, leaving the placentas 

 and ovules free in the centre; or by supposing that the placentas are 

 not marginal but axile formations, produced by an elongation of the 

 axis, the ovules being lateral buds, and the carpels verticillate leaves, 

 united together around the axis. The latter view has been sup- 

 ported by many botanists, and is confirmed by the fact, that in some 

 cases the placenta is actually prolonged beyond the carpels. The 

 first of these views would apply well to Caryophyllaceae, the second 

 to Primulaceae. In the latter case, the only way of explaining the 

 appearance on the marginal hypothesis, will be by considering the 

 placentas as formed from the carpels by a process of chorization (^[ 383), 

 and united together in the centre. 



444. Some indeed, as Schleiden and Endlicher, consider the axile 

 view of placentation as applicable to all cases, the axis in some cases 

 remaining free and independent, at other tunes sending prolongations 

 along the margins of the carpellary leaves, and thus forming the mar- 

 ginal placentas. The occurrence of placentas 

 over the whole inner surface of the carpels 

 or of the dissepiments, as in Nymphsa and 

 in Butomus umbellatus (figs. 393, 394); 

 also, though very rarely, along the dorsal 

 suture, as in Cabomba, or on lines within 

 the margin, as in Orobanche, has been 

 supposed to confirm this view. Schleiden 

 argues in favour of it, from the case of Ar- 

 meria, where there axe five carpels and 

 a single ovule attached to a cord, which 

 arises from the axis, and becomes curved at 

 the apex so as to suspend the ovule ; also, 



from cases, such as Taxus, where the ovule appears to be naked and 

 terminates a branch. 



445. This theory of placentation, however, cannot be easily applied 

 to all cases; and Gray says that it is disproved in cases of monstrosity, 

 in which the anther is changed into a carpel, or where one part of 

 the anther is thus transformed and bears ovules, while the other, 

 as well as the filament, remain unchanged. In the case of Luffa 

 foetida, the entangled fibres of the carpeUary leaves, even in the young 



Figs. 393, 394. One of the carpels of Butomus umbellatus, or flowering Rush, cut trans- 

 versely in 393, and longitudinally in 394-. I, Loculament or cavity of the carpel, o, Ovules. 

 s, Stigmata. 



