FERTILIZATION AND THE ORIGIN OF SEEDS 207 



consists of many free carpels. When the pistil consists 

 of one or more free carpels it is said to be apocarpous ; 

 and when of two or more carpels united together, it is syn- 

 carpous. If it arises above the other parts (calyx, corolla, 

 and stamens) it is superior, and if below, it is inferior. 



Sometimes botanists use the word ' pistil ' in a different 

 sense. When the carpels are free each consists typically 

 of an ovary, style, and stigma. Then 

 the flower is said to have many 

 pistils, e. g. the Buttercup ; but 

 when the carpels are joined, as in 

 the Stock and Tulip, the flower is 

 said to have only one pistil. The 

 name gynoecium is given to the 

 central part of the flower, whether 

 consisting of one carpel or many, 

 free or joined. 



The ovule and the embryo-sac. 

 When the ovule first appears on 

 the placenta it consists of a small 

 outgrowth of tissue, the nucellus 

 (Fig. 140, n) . Around the base of this, 

 two coats grow upwards and cover 

 the nucellus, with the exception of 

 a minute pore, which remains at the 

 end and forms the micropyle. Within 

 the nucellus a large cell arises, called 

 the embryo-sac (em), within which 



several cells are formed, one of these, near the micropyle, 

 being called the egg-cell. 



Fig. 140, 1-3, illustrates these points. In these the ovule 

 is represented as a straight one, but this form is not common. 

 More usually the ovule during its development becomes 

 bent and often inverted, so that the micropyle is brought 

 down to the base of the ovule stalk or funicle. Such an 



Fig. 139. Diagram 

 of opened Pistil. f, 

 funicle ; o, ovule ; ov , 

 ovary ; PI, placenta ; 

 Po, pollen -grains ; P.t, 

 pollen-tube ; s, stigma ; 

 sy, style. 



