THE PLACENTA 47 



Compound Pistils are composed of carpels which have united 

 to form them, and therefore will have just as many cells as carpels. 

 When each simple ovary has its placenta, or seed-bearing line, at 

 the inner angle the resulting compound ovary has as many axile 

 or central placentae as there are carpels, but all [more or less consoli- 

 dated into one. The partitions are called dissepiments and form part 

 of the walls of the ovary. If, however, the carpels are joined by their 

 edges, like the petals of a gamopetalous corolla, there will be but one 

 cell, and the placenta will be parietal, or on the wall. 



The OVULES are transformed buds, destined to become seeds in the 

 mature fruit. Their number varies from one to hundreds. In position, 

 they are erect, growing upward from the base of the ovary, as in the 

 Compositce; ascending turning upward from the side of the ovary or cell; 

 pendulous, like the last except that it turns downward; horizontal when 

 directed straight outward; suspended, hanging perpendicularly from the 

 top of the ovary. 



In Gymnosperms the ovules are naked; in Angiosperms they are 

 enclosed in a seed vessel. 



A complete angiospermous seed ovule consists of a nucellus or 

 body ; two coats, the outer or primine, and the inner or secundine ; and 

 a FUNICULUS, or stalk. Within the nucellus is found the embryo sac 

 containing the ovum or female reproductive cell. 



The coats do not completely envelop the nucellus, but an opening 

 at the apex, called the poramen or micropyle admits the pollen tube. 

 The point where the coats are attached to each other and to the nucellus 

 is called the chalaza. The hilum marks the point where the funiculus 

 is joined to the ovule, and if attached to the ovule through a part of its 

 length, the adherent portion is called the raphe. The shape of the 

 ovule may be orthotropous, or straight; campylotropous, bent or 

 curved; amphitropous, partly inverted; and anatropous, inverted. 

 The last two forms are most common. A campylotropous ovule is one 

 whose body is bent so that the hilum and micropyle are approximated. 



The Placenta 



The placenta is the nutritive tissue connecting the ovules with the 

 wall of the ovary. The various types of placenta arrangement (pla- 

 centation) are grouped according to their relative complexity as 

 follows : 



