152 COMPOUND ORGANS OP PLANTS. 



margins turned inwards, yet not so as to meet in the centre of 

 the ovary, to cohere merely by their contiguous inflexed por- 



Fig. 55. 



tions, a one-celled tri-carpellary ovary would result, with three 

 imperfect dissepiments projecting into its cavity, in Fig. 55, a. 

 If we imagine the margins of three carpellary leaves to cohere, 

 making only three slight introflexions, it is obvious that there 

 would be no dissepiments, and the placentas would be truly 

 parietal (paries a wall) the ovules being borne directly on the 

 walls of the ovary, as at b. If, on the contrary, we suppose 

 the three carpellary leaves to be so folded inwardly as to carry 

 the inflexed portions of their united lamina, or in other words, 

 their dissepiments to the centre, and the dissepiments there 

 to unite and form a common axis, about which the ovules 

 develope; and if we then imagine the walls of the dissepiments 

 to be ruptured by the rapid growth of the ovary, it is obvious 

 that we shall have what is called a free central placenta, as 

 shown at c, Fig. 55, and also in Fig. 56. In all these cases the 

 compound pistil has an unilocular ovary. 



All gradations may be observed in nature between strictly 

 parietal placenta and those which are carried forward so as to 

 meet in the centre of the ovary and separate its cavity into 

 distinct cells. 



la the Dog's-tooth violet (Erythronium) and Campanula the 

 walls of the dissepiments are not ruptured. Fig. 55 is a tra- 



