PLACENTATION. 483 



that the carpels are invaginated ^vithin the expanded 

 top of the flower-stalk and more or less adherent to it. 

 Some of the gourds afford good illustrations of this, the 

 upper part of the carpels in these fruits projecting 

 beyond the axial portion. But this matter loses much 

 of its importance if the morphological identity of axis 

 and leaf-organ be conceded. The carpels in inferior 

 ovaries seldom or never correspond to the lamina of the 

 leaf, and between the vaginal portion of the carpellary 

 leaf, and the axis who shall draw the distinction ? 



Placentation. Some botanists have considered the 

 placentas to be portions of the carpel, and have com- 

 pared the production of ovules on them to the forma- 

 tion of buds on the leaf of Bryophijllum. Others 

 have been led to see in each placenta, even when 

 it is, to all outward appearance, a portion of the car- 

 pellary leaf, a direct prolongation from the axis, ad- 

 herent to the leaf. Teratology shows that ovules may 

 be formed in differently on leaf-organs or on stem-organs. 

 Sutural, parietal, axile, free-central placentation, and, if 

 there be more forms, all may be met with even in the 

 same ovary (see pp. 96, 508). Now, if there were sxich 

 special tendencies in the axis, as contrasted with the 

 leaf, to produce ovules, it is hardly likely that such 

 anomalous arrangements as those just mentioned 

 would be as frequent as they are. But as leaves 

 produce other leaves, from their edges or their 

 surfaces, and as they form buds in the same situations, 

 just as axial organs do,^ there is surely little ground 

 for considering the placentas, or ovuliferous portions 

 of the plant, to be of necessity axial. Here again, 

 much of the difficulty vanishes if the morphological 



' It must, however, be borne in mind that no true Icof-organ has jot 

 been seen with a bud at its exact apex (unless it be the uepaul barley), 

 while in the case of an axial organ such a jx>iiition of the bud is 

 constant. The nearest approach is in the case of impari-pinnatc leaves 

 in which the terminal leatlut is jointed to the common rachis, and in 

 the leaves of some Meliacece which continue to push forth new leaflcta 

 even after the leaf has attained maturity. 



