OVULES. 



43 



87. The placentas are developed at each of the two edges of 

 the carpellary leaf If these edges be in their normal condi- 

 tions, that is, united, there will be apparently but one placenta 

 to the carpel, and that central. But if the edges be separate, 

 there will necessarily be two placent^e to each carpel, the one 

 to the right and the other to the left of the dorsal suture and 

 style. They are then said to be parietal {paries, a wall). 



FIG. 11. — 1, Cross section of a one-celled, three-carpelled ovary with parietal placentas, 

 the dissepiments partially obliterated ; 2, dissepiments wholly obliterated; 3, dissepiments 

 obliterated, showing a free central placenta ; 4, a five-celled ovary with 5 false dissepiments, 

 as in the flax; 5, vertical section of an ovary with parietal placentoE ; 6, with free central pla- 

 centae ; 7, an amphitropous ovule ; 8, vertical section of the same ; a, funiculus ; 6, raphe ; 

 c, chalaza ; </, nucleus ; e, secundine ; f, primine ; g, micropyle ; 9, anatropous ovules at- 

 tached to the ovar)'. 



88. But the placenta? are sometimes found in the common 

 centre when there are no dissepiments (Fig. 11; 3,6). This 

 anomaly, which is called a free central placenta, is thus ex- 

 plained. The dissepiments were at first actually formed in the 

 usual manner, but afterwards, by the rapid expansion of the 

 shell, they were torn away and obliterated. 



a. As the ovules are always developed by the placentoe, they, of cotirse, grow 

 out of the margins of the carpellaiy leaf, and are, therefore, understood to be 

 analogous to buds. For, in the Bryophyllum, and some other plants, the true 

 leaves do habitually develop buds at their margins (Fig. 10; 8), and in the mign- 

 ionette the ovules themselves have been seen transformed into leaves. 



89. The ovules are almost always enclosed in the ovary. In 

 the mignionette they are partially naked, and in the fir tribe, 

 Coniferee, entirely so, the carpellary leaf being open or wanting. 



