XIIl] PL AGENT ATION 115 



all such characters it must be used together with others. 

 Still the character is useful as an indication e.g. all the 

 Umbelliferae have pendulous anatropous ovules with a 

 vertical raphe, and the same with the closely allied 

 Araliacese and Cornacese. In the allied Caprifoliacese, 

 however, both dorsal and ventral raphe occur, with similar 

 ovules. 



The typical place of origin of the ovule is, as we have 

 seen, the margin of the carpel, and in the vast majority 

 of cases this is where it occurs, the insertion (placentation) 

 as regards the ovary or carpellary leaf differing according 

 as the carpels are free (marginal placentation) or syn- 

 carpous (parietal and axile placentation, &c.). In rare 

 cases the ovule terminates the floral axis as in Taxus, 

 Naias, Piper, Polygonum, or is produced just beneath the 

 actual apex as in Composita?, Primulaceae. In a few rare 

 instances the ovules arise from the surface of the inner 

 walls of the ovary (Butomus, Nymphcea), and the placen- 

 tation is superficial. 



Several cases, formerly doubtful, turn out to obey the 

 general rule that the placentation is originally marginal. 

 In Mesemhryantliemum the ovules arise in the young 

 ovary on the inner margins of the infolded carpels, but 

 by displacements later they come to appear on the outer 

 walls and as if from the dorsal sutures, and similar cases 

 occur in Punica and Melastomacece. 



In the free-central placentas of Caryophyllacese and 

 Primulacese, again, the ovules do not spring from the axis, 

 but from the basal portions of the carpels. Since these 

 cases do not concern the plants here treated, however, 

 I pass by the details. 



When the young carpel has attained the stage of 

 a definite flattened or curved outgrowth of embryonic 

 tissue, either free or joined to neighbouring carpels, one 



82 



